CVE-2021-27850 (GCVE-0-2021-27850)
Vulnerability from cvelistv5 – Published: 2021-04-15 07:40 – Updated: 2024-08-03 21:33Title
Bypass of the fix for CVE-2019-0195
Summary
A critical unauthenticated remote code execution vulnerability was found all recent versions of Apache Tapestry. The affected versions include 5.4.5, 5.5.0, 5.6.2 and 5.7.0. The vulnerability I have found is a bypass of the fix for CVE-2019-0195. Recap: Before the fix of CVE-2019-0195 it was possible to download arbitrary class files from the classpath by providing a crafted asset file URL. An attacker was able to download the file `AppModule.class` by requesting the URL `http://localhost:8080/assets/something/services/AppModule.class` which contains a HMAC secret key. The fix for that bug was a blacklist filter that checks if the URL ends with `.class`, `.properties` or `.xml`. Bypass: Unfortunately, the blacklist solution can simply be bypassed by appending a `/` at the end of the URL: `http://localhost:8080/assets/something/services/AppModule.class/` The slash is stripped after the blacklist check and the file `AppModule.class` is loaded into the response. This class usually contains the HMAC secret key which is used to sign serialized Java objects. With the knowledge of that key an attacker can sign a Java gadget chain that leads to RCE (e.g. CommonsBeanUtils1 from ysoserial). Solution for this vulnerability: * For Apache Tapestry 5.4.0 to 5.6.1, upgrade to 5.6.2 or later. * For Apache Tapestry 5.7.0, upgrade to 5.7.1 or later.
Severity
9.8 (Critical)
Assigner
References
3 references
| URL | Tags |
|---|---|
| https://lists.apache.org/thread.html/r237ff7f286b… | x_refsource_MISC |
| http://www.openwall.com/lists/oss-security/2021/04/15/1 | mailing-listx_refsource_MLIST |
| https://security.netapp.com/advisory/ntap-2021052… | x_refsource_CONFIRM |
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Apache Software Foundation | Apache Tapestry |
Affected:
Apache Tapestry 5.5.0
Affected: Apache Tapestry 5.7.0 Affected: Apache Tapestry 5.4.5 , < Apache Tapestry 5.4.0* (custom) Affected: Apache Tapestry 5.6.2 , < Apache Tapestry 5.6.0* (custom) |
guessed |
Shadowserver
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: db98cb31-36f0-4d78-9ea0-7ccabb3bbf8c
Exploited: Yes
Characteristics
Severity:
98.0
Timestamps
First Seen: 2023-10-14
Asserted: 2023-10-14
Last Seen: 2026-07-19
Scope
Asset Exposure: ['internet-facing']
Notes: Affected: Apache / Tapestry | Class: web-app-framework | Severity: Critical (CVSS 9.8) | IoT: no | In CISA KEV: no | Honeypot connections on 2026-07-19: 1
Evidence
Type: Honeypot
Signal: In The Wild Attempts
Confidence: 70%
Source: shadowserver
Details
| 1D | 1 |
|---|---|
| Iot | no |
| Feed | Shadowserver Foundation honeypot/exploited-vulnerabilities |
| Type | http-scan |
| Class | web-app-framework |
| 7D Avg | 1 |
| Vendor | Apache |
| 30D Avg | 4 |
| 90D Avg | 4 |
| Product | Tapestry |
| Cisa Kev | no |
| Connections | 1 |
| Observation Date | 2026-07-19 |
| Vulnerability Class | CVSS |
| Vulnerability Score | 9.8 |
| Vulnerability Severity | Critical |
References
Created: 2026-06-30 09:22 UTC
| Updated: 2026-07-21 01:01 UTC
Previdian
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: f0da9e81-d45f-4f65-be6a-fd4af53b9c04
Exploited: Yes
Timestamps
First Seen: 2025-04-28
Asserted: 2025-04-28
Scope
Notes: KEVIntel entry: Bypass of the fix for CVE-2019-0195 | Affected: Apache Software Foundation / Apache Tapestry | CVSS: 9.8 (CRITICAL) | Used in malware: unknown | Not yet in CISA KEV: True
Evidence
Type: Public Report
Signal: Successful Exploitation
Confidence: 70%
Source: kevintel
Details
| Feed | KEVIntel (kevintel.com) |
|---|---|
| Title | Bypass of the fix for CVE-2019-0195 |
| Vendor | Apache Software Foundation |
| Product | Apache Tapestry |
| Added Date | 2025-04-28T00:00:00.000Z |
| Cvss Score | 9.8 |
| Epss Score | None |
| Cvss Severity | CRITICAL |
| Epss Percentile | None |
| Used In Malware | unknown |
| Ahead Of Cisa Kev | None |
| Not Yet In Cisa Kev | True |
References
Created: 2026-06-23 14:04 UTC
| Updated: 2026-07-10 06:14 UTC
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"value": "Se encontr\u00f3 una vulnerabilidad cr\u00edtica de ejecuci\u00f3n de c\u00f3digo remota no autenticado en todas las versiones recientes de Apache Tapestry.\u0026#xa0;Las versiones afectadas incluyen 5.4.5, 5.5.0, 5.6.2 y 5.7.0.\u0026#xa0;La vulnerabilidad encontrada es un desv\u00edo de la soluci\u00f3n para CVE-2019-0195.\u0026#xa0;Resumen: versiones anteriores a correcci\u00f3n de CVE-2019-0195, era posible descargar archivos de clases arbitrarios desde la ruta de clases proporcionando una URL de archivo de activos dise\u00f1ada.\u0026#xa0;Un atacante pudo descargar el archivo \"AppModule.class\" al requerir la URL \"http://localhost:8080/assets/something/services/AppModule.class\" que contiene una clave secreta HMAC.\u0026#xa0;La correcci\u00f3n para ese error fue un filtro de lista negra que verifica si la URL termina con \".class\",\" properties\" o \".xml\".\u0026#xa0;Omitir: Desafortunadamente, la soluci\u00f3n de lista negra puede simplemente ser omitida al agregar un \"/` al final de la URL: \"http: // localhost:8080/assets/something/services/AppModule.class/\". La barra es eliminada despu\u00e9s de la comprobaci\u00f3n de la lista negra y el archivo` AppModule.class` se carga en la respuesta.\u0026#xa0;Esta clase generalmente contiene la clave secreta HMAC que es usada para firmar objetos Java serializados.\u0026#xa0;Con el conocimiento de esa clave, un atacante puede firmar una cadena de dispositivos Java que conlleva a una RCE (por ejemplo, CommonsBeanUtils1 de ysoserial).\u0026#xa0;Soluci\u00f3n para esta vulnerabilidad: *Para Apache Tapestry versiones 5.4.0 hasta 5.6.1, actualice a versiones 5.6.2 o posteriores.\u0026#xa0;*Para Apache Tapestry versi\u00f3n 5.7.0, actualice a versiones 5.7.1 o posteriores"
}
],
"id": "CVE-2021-27850",
"lastModified": "2024-11-21T05:58:38.010",
"metrics": {
"cvssMetricV2": [
{
"acInsufInfo": false,
"baseSeverity": "HIGH",
"cvssData": {
"accessComplexity": "LOW",
"accessVector": "NETWORK",
"authentication": "NONE",
"availabilityImpact": "COMPLETE",
"baseScore": 10.0,
"confidentialityImpact": "COMPLETE",
"integrityImpact": "COMPLETE",
"vectorString": "AV:N/AC:L/Au:N/C:C/I:C/A:C",
"version": "2.0"
},
"exploitabilityScore": 10.0,
"impactScore": 10.0,
"obtainAllPrivilege": false,
"obtainOtherPrivilege": false,
"obtainUserPrivilege": false,
"source": "nvd@nist.gov",
"type": "Primary",
"userInteractionRequired": false
}
],
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "HIGH",
"baseScore": 9.8,
"baseSeverity": "CRITICAL",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"exploitabilityScore": 3.9,
"impactScore": 5.9,
"source": "nvd@nist.gov",
"type": "Primary"
}
]
},
"published": "2021-04-15T08:15:14.823",
"references": [
{
"source": "security@apache.org",
"tags": [
"Exploit",
"Mailing List",
"Third Party Advisory"
],
"url": "http://www.openwall.com/lists/oss-security/2021/04/15/1"
},
{
"source": "security@apache.org",
"tags": [
"Mailing List",
"Vendor Advisory"
],
"url": "https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3E"
},
{
"source": "security@apache.org",
"tags": [
"Third Party Advisory"
],
"url": "https://security.netapp.com/advisory/ntap-20210528-0002/"
},
{
"source": "af854a3a-2127-422b-91ae-364da2661108",
"tags": [
"Exploit",
"Mailing List",
"Third Party Advisory"
],
"url": "http://www.openwall.com/lists/oss-security/2021/04/15/1"
},
{
"source": "af854a3a-2127-422b-91ae-364da2661108",
"tags": [
"Mailing List",
"Vendor Advisory"
],
"url": "https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3E"
},
{
"source": "af854a3a-2127-422b-91ae-364da2661108",
"tags": [
"Third Party Advisory"
],
"url": "https://security.netapp.com/advisory/ntap-20210528-0002/"
}
],
"sourceIdentifier": "security@apache.org",
"vulnStatus": "Modified",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-200"
},
{
"lang": "en",
"value": "CWE-502"
}
],
"source": "security@apache.org",
"type": "Secondary"
},
{
"description": [
{
"lang": "en",
"value": "CWE-502"
}
],
"source": "nvd@nist.gov",
"type": "Primary"
}
]
}
},
"redhat_vex": {
"current_release_date": "2026-03-27T14:23:32+00:00",
"cve": "CVE-2021-27850",
"id": "CVE-2021-27850",
"initial_release_date": "2021-01-01T00:00:00+00:00",
"product_status:known_not_affected": "1",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "Bypass of the fix for CVE-2019-0195",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-27850.json",
"version": "3"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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