CWE-506
Allowed-with-ReviewEmbedded Malicious Code
Abstraction: Class · Status: Incomplete
The product contains code that appears to be malicious in nature.
548 vulnerabilities reference this CWE, most recent first.
GHSA-8QM2-24QC-C4QG
Vulnerability from github – Published: 2020-09-01 19:57 – Updated: 2021-09-24 17:32Version 0.0.6 of freshdom contained malicious code. The code when executed in the browser would enumerate password, cvc, cardnumber fields from forms and send the extracted values to https://js-metrics.com/minjs.php?pl=
Recommendation
If version 0.0.6 of this module is found installed you will want to replace it with a version before or after 0.0.6. In addition to replacing the installed module, you will also want to evaluate your application to determine whether or not user data was compromised.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "freshdom"
},
"versions": [
"0.0.6"
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-506"
],
"github_reviewed": true,
"github_reviewed_at": "2020-08-31T18:30:26Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "Version 0.0.6 of `freshdom` contained malicious code. The code when executed in the browser would enumerate password, cvc, cardnumber fields from forms and send the extracted values to `https://js-metrics.com/minjs.php?pl=`\n\n\n\n## Recommendation\n\nIf version 0.0.6 of this module is found installed you will want to replace it with a version before or after 0.0.6. In addition to replacing the installed module, you will also want to evaluate your application to determine whether or not user data was compromised.",
"id": "GHSA-8qm2-24qc-c4qg",
"modified": "2021-09-24T17:32:50Z",
"published": "2020-09-01T19:57:56Z",
"references": [
{
"type": "PACKAGE",
"url": "https://github.com/jamiller619/freshdom"
},
{
"type": "WEB",
"url": "https://snyk.io/vuln/SNYK-JS-FRESHDOM-450987"
},
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/627"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Malicious Package in freshdom"
}
GHSA-8QP3-PVWC-2G4P
Vulnerability from github – Published: 2018-07-23 20:49 – Updated: 2023-09-08 20:34The nodefabric package is a piece of malware that steals environment variables and sends them to attacker controlled locations.
All versions have been unpublished from the npm registry.
Recommendation
As this package is malware, if you find it installed in your environment, the real security concern is determining how it got there.
If you have found this installed in your environment, you should: 1. Delete the package 2. Clear your npm cache 3. Ensure it is not present in any other package.json files on your system 4. Regenerate your registry credentials, tokens, and any other sensitive credentials that may have been present in your environment variables.
Additionally, any service which may have been exposed via credentials in your environment variables, such as a database, should be reviewed for indicators of compromise as well.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "nodefabric"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"last_affected": "1.0.2"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2017-16054"
],
"database_specific": {
"cwe_ids": [
"CWE-506"
],
"github_reviewed": true,
"github_reviewed_at": "2020-06-16T21:26:26Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "The `nodefabric` package is a piece of malware that steals environment variables and sends them to attacker controlled locations. \n\nAll versions have been unpublished from the npm registry.\n\n\n## Recommendation\n\n\n\nAs this package is malware, if you find it installed in your environment, the real security concern is determining how it got there. \n\nIf you have found this installed in your environment, you should:\n1. Delete the package\n2. Clear your npm cache\n3. Ensure it is not present in any other package.json files on your system\n4. Regenerate your registry credentials, tokens, and any other sensitive credentials that may have been present in your environment variables. \n\nAdditionally, any service which may have been exposed via credentials in your environment variables, such as a database, should be reviewed for indicators of compromise as well.",
"id": "GHSA-8qp3-pvwc-2g4p",
"modified": "2023-09-08T20:34:44Z",
"published": "2018-07-23T20:49:58Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2017-16054"
},
{
"type": "ADVISORY",
"url": "https://github.com/advisories/GHSA-8qp3-pvwc-2g4p"
},
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/488"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
"type": "CVSS_V3"
}
],
"summary": "nodefabric is malware"
}
GHSA-8QX4-R7FX-XC4V
Vulnerability from github – Published: 2020-09-11 21:08 – Updated: 2021-10-01 14:08All versions of requst typosquatted a popular package of similar name and tracked users who had installed the incorrect package. The package uploaded information to a remote server including: name of the downloaded package, name of the intended package, the Node version and whether the process was running as sudo. There is no further compromise.
Recommendation
Remove the package from your dependencies and always ensure package names are typed correctly upon installation.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "requst"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-506"
],
"github_reviewed": true,
"github_reviewed_at": "2020-08-31T18:38:41Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "All versions of `requst` typosquatted a popular package of similar name and tracked users who had installed the incorrect package. The package uploaded information to a remote server including: name of the downloaded package, name of the intended package, the Node version and whether the process was running as sudo. There is no further compromise.\n\n\n## Recommendation\n\nRemove the package from your dependencies and always ensure package names are typed correctly upon installation.",
"id": "GHSA-8qx4-r7fx-xc4v",
"modified": "2021-10-01T14:08:31Z",
"published": "2020-09-11T21:08:19Z",
"references": [
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/865"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Malicious Package in requst"
}
GHSA-8RXG-9G6F-VQ9P
Vulnerability from github – Published: 2020-09-01 19:46 – Updated: 2023-12-07 22:07Version 4.1.48 of another-date-range-picker contained malicious code. The code when executed in the browser would enumerate password, cvc, cardnumber fields from forms and send the extracted values to https://js-metrics.com/minjs.php?pl=
Recommendation
If version 4.1.48 of this module is found installed you will want to replace it with a version before or after 4.1.48. In addition to replacing the installed module, you will also want to evaluate your application to determine whether or not user data was compromised.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "another-date-range-picker"
},
"versions": [
"4.1.48"
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-506"
],
"github_reviewed": true,
"github_reviewed_at": "2020-08-31T18:30:03Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "Version 4.1.48 of `another-date-range-picker` contained malicious code. The code when executed in the browser would enumerate password, cvc, cardnumber fields from forms and send the extracted values to `https://js-metrics.com/minjs.php?pl=`\n\n\n## Recommendation\n\nIf version 4.1.48 of this module is found installed you will want to replace it with a version before or after 4.1.48. In addition to replacing the installed module, you will also want to evaluate your application to determine whether or not user data was compromised.",
"id": "GHSA-8rxg-9g6f-vq9p",
"modified": "2023-12-07T22:07:29Z",
"published": "2020-09-01T19:46:01Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/bi-a/mydaterangepicker"
},
{
"type": "PACKAGE",
"url": "https://github.com/kekeh/mydaterangepicker"
},
{
"type": "WEB",
"url": "https://snyk.io/vuln/SNYK-JS-ANOTHERDATERANGEPICKER-451011"
},
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/617"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Malicious Package in another-date-range-picker"
}
GHSA-8VJ3-JGCF-77JV
Vulnerability from github – Published: 2020-09-02 20:26 – Updated: 2021-10-01 14:04All versions of requeest typosquatted a popular package of similar name and tracked users who had installed the incorrect package. The package uploaded information to a remote server including: name of the downloaded package, name of the intended package, the Node version and whether the process was running as sudo. There is no further compromise.
Recommendation
Remove the package from your dependencies and always ensure package names are typed correctly upon installation.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "requeest"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-506"
],
"github_reviewed": true,
"github_reviewed_at": "2020-08-31T18:38:25Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "All versions of `requeest` typosquatted a popular package of similar name and tracked users who had installed the incorrect package. The package uploaded information to a remote server including: name of the downloaded package, name of the intended package, the Node version and whether the process was running as sudo. There is no further compromise.\n\n\n## Recommendation\n\nRemove the package from your dependencies and always ensure package names are typed correctly upon installation.",
"id": "GHSA-8vj3-jgcf-77jv",
"modified": "2021-10-01T14:04:42Z",
"published": "2020-09-02T20:26:49Z",
"references": [
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/858"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Malicious Package in requeest"
}
GHSA-8W9J-6WG6-QV4F
Vulnerability from github – Published: 2020-09-03 19:41 – Updated: 2021-09-30 20:13This package contained malicious code. The package uploaded system information such as OS and hostname to a remote server.
Recommendation
Remove the package from your environment. There are no indications of further compromise.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "axioss"
},
"ranges": [
{
"events": [
{
"introduced": "0.0.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-506"
],
"github_reviewed": true,
"github_reviewed_at": "2020-08-31T18:48:06Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "This package contained malicious code. The package uploaded system information such as OS and hostname to a remote server.\n\n\n## Recommendation\n\nRemove the package from your environment. There are no indications of further compromise.",
"id": "GHSA-8w9j-6wg6-qv4f",
"modified": "2021-09-30T20:13:23Z",
"published": "2020-09-03T19:41:17Z",
"references": [
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/1124"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Malicious Package in axioss"
}
GHSA-9272-59X2-GWF2
Vulnerability from github – Published: 2020-09-03 17:04 – Updated: 2021-10-01 21:04All versions of this package contained malware. The package was designed to find and exfiltrate cryptocurrency wallets.
Recommendation
Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer.
The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "ripedm160"
},
"ranges": [
{
"events": [
{
"introduced": "0.0.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-506"
],
"github_reviewed": true,
"github_reviewed_at": "2020-08-31T18:58:05Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "All versions of this package contained malware. The package was designed to find and exfiltrate cryptocurrency wallets.\n\n\n## Recommendation\n\nAny computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer.\n\nThe package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.",
"id": "GHSA-9272-59x2-gwf2",
"modified": "2021-10-01T21:04:39Z",
"published": "2020-09-03T17:04:13Z",
"references": [
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/1404"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
"type": "CVSS_V3"
}
],
"summary": "Malicious Package in ripedm160"
}
GHSA-9298-M7JF-55H2
Vulnerability from github – Published: 2020-09-04 16:42 – Updated: 2021-10-01 20:43All versions of this package contained malware. The package was designed to find and exfiltrate cryptocurrency wallets.
Recommendation
Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer.
The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "bitconid-rpc"
},
"ranges": [
{
"events": [
{
"introduced": "0.0.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-506"
],
"github_reviewed": true,
"github_reviewed_at": "2020-08-31T18:56:44Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "All versions of this package contained malware. The package was designed to find and exfiltrate cryptocurrency wallets.\n\n\n## Recommendation\n\nAny computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer.\n\nThe package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.",
"id": "GHSA-9298-m7jf-55h2",
"modified": "2021-10-01T20:43:38Z",
"published": "2020-09-04T16:42:08Z",
"references": [
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/1369"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
"type": "CVSS_V3"
}
],
"summary": "Malicious Package in bitconid-rpc"
}
GHSA-92PX-Q4W8-HRR5
Vulnerability from github – Published: 2020-09-01 19:56 – Updated: 2021-09-24 18:30Version 1.1.7 of impala contained malicious code. The code when executed in the browser would enumerate password, cvc, cardnumber fields from forms and send the extracted values to https://js-metrics.com/minjs.php?pl=
Recommendation
If version 1.1.7 of this module is found installed you will want to replace it with a version before or after 1.1.7. In addition to replacing the installed module, you will also want to evaluate your application to determine whether or not user data was compromised.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "impala"
},
"versions": [
"1.1.7"
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-506"
],
"github_reviewed": true,
"github_reviewed_at": "2020-08-31T18:30:28Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "Version 1.1.7 of `impala` contained malicious code. The code when executed in the browser would enumerate password, cvc, cardnumber fields from forms and send the extracted values to `https://js-metrics.com/minjs.php?pl=`\n\n\n\n## Recommendation\n\nIf version 1.1.7 of this module is found installed you will want to replace it with a version before or after 1.1.7. In addition to replacing the installed module, you will also want to evaluate your application to determine whether or not user data was compromised.",
"id": "GHSA-92px-q4w8-hrr5",
"modified": "2021-09-24T18:30:53Z",
"published": "2020-09-01T19:56:52Z",
"references": [
{
"type": "PACKAGE",
"url": "https://github.com/shenfw1987/impala"
},
{
"type": "WEB",
"url": "https://snyk.io/vuln/SNYK-JS-IMPALA-450989"
},
{
"type": "WEB",
"url": "https://www.npmjs.com/advisories/628"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "Malicious Package in impala"
}
GHSA-93QJ-5Q5V-3C2H
Vulnerability from github – Published: 2026-08-26 14:36 – Updated: 2026-08-26 14:36Summary
The PyPI account that publishes pantheon-agents was compromised in the June 2026 "Hades" PyPI supply-chain attack (Mini Shai-Hulud / Miasma lineage). The attacker used a stolen, long-lived PyPI API token to upload trojanized releases pantheon-agents 0.6.1 and 0.6.2 directly to PyPI.
Only the PyPI artifacts are affected. The GitHub source repository, its git tags, and all other distribution channels are clean — no malicious code was committed to the repository.
Affected
pantheon-agents0.6.1 and 0.6.2 on PyPI.
Not affected: installs from the GitHub source, version 0.6.0 and earlier, and the Desktop / Online apps.
Indicators of compromise
The malicious wheels ship a *-setup.pth file that executes on Python startup. It downloads the Bun JavaScript runtime and runs an obfuscated credential stealer (_index.js) that harvests and exfiltrates credentials reachable from the host — environment variables, ~/.pypirc, ~/.npmrc, cloud credentials (~/.aws, etc.), SSH keys, and API tokens.
Check your environment's site-packages for an unexpected *-setup.pth, and your home directory for _index.js or a Bun runtime (~/.bun).
Impact
Anyone who pip installed pantheon-agents 0.6.1 or 0.6.2 should assume every credential present on that machine has been exfiltrated.
Remediation
- Do not install
pantheon-agentsfrom PyPI until distribution resumes. - If you installed 0.6.1 or 0.6.2:
- Run
pip uninstall pantheon-agentsimmediately and check for the IoCs above. - Rotate every credential that was present on that machine (API keys, tokens, SSH keys, cloud credentials).
- Install only from the clean GitHub source:
pip install "git+https://github.com/aristoteleo/PantheonOS.git"
Status
The PyPI account is suspended and the malicious token has been disabled. PyPI distribution will resume after account recovery and migration to PyPI Trusted Publishing (OIDC). Sibling projects by the same maintainer (e.g. executor-engine, funcdesc, cmd2func, pantheon-toolsets, coolbox, ufish, magique, executor-http) were hit by the same campaign and are being remediated separately.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 0.6.2"
},
"package": {
"ecosystem": "PyPI",
"name": "pantheon-agents"
},
"ranges": [
{
"events": [
{
"introduced": "0.6.1"
},
{
"fixed": "0.6.4"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-506",
"CWE-522"
],
"github_reviewed": true,
"github_reviewed_at": "2026-08-26T14:36:45Z",
"nvd_published_at": null,
"severity": "CRITICAL"
},
"details": "## Summary\nThe PyPI account that publishes `pantheon-agents` was compromised in the June 2026 \"Hades\" PyPI supply-chain attack (Mini Shai-Hulud / Miasma lineage). The attacker used a stolen, long-lived PyPI API token to upload **trojanized releases `pantheon-agents` 0.6.1 and 0.6.2 directly to PyPI**.\n\n**Only the PyPI artifacts are affected.** The GitHub source repository, its git tags, and all other distribution channels are clean \u2014 no malicious code was committed to the repository.\n\n## Affected\n- `pantheon-agents` **0.6.1** and **0.6.2** on PyPI.\n\nNot affected: installs from the GitHub source, version 0.6.0 and earlier, and the Desktop / Online apps.\n\n## Indicators of compromise\nThe malicious wheels ship a `*-setup.pth` file that executes on Python startup. It downloads the Bun JavaScript runtime and runs an obfuscated credential stealer (`_index.js`) that harvests and exfiltrates credentials reachable from the host \u2014 environment variables, `~/.pypirc`, `~/.npmrc`, cloud credentials (`~/.aws`, etc.), SSH keys, and API tokens.\n\nCheck your environment\u0027s `site-packages` for an unexpected `*-setup.pth`, and your home directory for `_index.js` or a Bun runtime (`~/.bun`).\n\n## Impact\nAnyone who `pip install`ed `pantheon-agents` 0.6.1 or 0.6.2 should assume **every credential present on that machine has been exfiltrated.**\n\n## Remediation\n1. **Do not install `pantheon-agents` from PyPI** until distribution resumes.\n2. If you installed 0.6.1 or 0.6.2:\n - Run `pip uninstall pantheon-agents` immediately and check for the IoCs above.\n - **Rotate every credential** that was present on that machine (API keys, tokens, SSH keys, cloud credentials).\n3. Install only from the clean GitHub source:\n ```\n pip install \"git+https://github.com/aristoteleo/PantheonOS.git\"\n ```\n\n## Status\nThe PyPI account is suspended and the malicious token has been disabled. PyPI distribution will resume after account recovery and migration to PyPI Trusted Publishing (OIDC). Sibling projects by the same maintainer (e.g. executor-engine, funcdesc, cmd2func, pantheon-toolsets, coolbox, ufish, magique, executor-http) were hit by the same campaign and are being remediated separately.",
"id": "GHSA-93qj-5q5v-3c2h",
"modified": "2026-08-26T14:36:45Z",
"published": "2026-08-26T14:36:45Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/aristoteleo/PantheonOS/security/advisories/GHSA-93qj-5q5v-3c2h"
},
{
"type": "PACKAGE",
"url": "https://github.com/aristoteleo/PantheonOS"
}
],
"schema_version": "1.4.0",
"severity": [],
"summary": "Trojanized pantheon-agents 0.6.1 and 0.6.2 on PyPI ship a credential stealer (supply-chain account compromise)"
}
Mitigation
Remove the malicious code and start an effort to ensure that no more malicious code exists. This may require a detailed review of all code, as it is possible to hide a serious attack in only one or two lines of code. These lines may be located almost anywhere in an application and may have been intentionally obfuscated by the attacker.
CAPEC-442: Infected Software
An adversary adds malicious logic, often in the form of a computer virus, to otherwise benign software. This logic is often hidden from the user of the software and works behind the scenes to achieve negative impacts. Many times, the malicious logic is inserted into empty space between legitimate code, and is then called when the software is executed. This pattern of attack focuses on software already fielded and used in operation as opposed to software that is still under development and part of the supply chain.
CAPEC-448: Embed Virus into DLL
An adversary tampers with a DLL and embeds a computer virus into gaps between legitimate machine instructions. These gaps may be the result of compiler optimizations that pad memory blocks for performance gains. The embedded virus then attempts to infect any machine which interfaces with the product, and possibly steal private data or eavesdrop.
CAPEC-636: Hiding Malicious Data or Code within Files
Files on various operating systems can have a complex format which allows for the storage of other data, in addition to its contents. Often this is metadata about the file, such as a cached thumbnail for an image file. Unless utilities are invoked in a particular way, this data is not visible during the normal use of the file. It is possible for an attacker to store malicious data or code using these facilities, which would be difficult to discover.