CVE-2026-66296 (GCVE-0-2026-66296)
Vulnerability from cvelistv5 – Published: 2026-08-03 19:04 – Updated: 2026-08-03 19:50
VLAI
EPSS
VEX
Title
Reflected XSS in oaskit's default HTML error handler
Summary
Improper Neutralization of Input During Web Page Generation (XSS) vulnerability in lud oaskit allows reflected cross-site scripting via the default HTML error handler.
Oaskit.ErrorHandler.Default.format_reason/4 and Oaskit.ErrorHandler.Default.reason_to_html/1 in lib/oaskit/error_handler/default.ex render request-validation failures as an HTML page whenever the request's Accept header contains html, interpolating request-controlled strings into that page without HTML escaping. The unescaped values are object keys taken from a request body or from an object or deepObject query parameter, which appear in the JSON Schema error's instance path when a schema rejects them (for example under additionalProperties: false), and the raw Content-Type header, reflected in unsupported-media-type errors when it fails to parse.
Because browsers send Accept: text/html on ordinary top-level navigation, a crafted GET link is sufficient to trigger the error page; no form submission, custom Content-Type, or attacker-controlled script on the victim's side is required. A payload such as filter[</code></h2><script>alert(document.domain)</script>]=x terminates the enclosing markup and the injected script executes in the origin of the application using oaskit, giving it access to that origin's cookies, session, and same-origin responses.
Both HTML error rendering and the vulnerable handler are enabled by default: Oaskit.Plugs.ValidateRequest defaults :html_errors to true and :error_handler to Oaskit.ErrorHandler.Default, so applications following the documented usage are affected without any opt-in.
This issue affects oaskit: from 0.1.0 before 0.14.1.
Severity
SSVC
Exploitation: poc
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-03 19:50 UTC
CWE
- CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://github.com/lud/oaskit/security/advisories… | vendor-advisoryrelated |
| https://cna.erlef.org/cves/CVE-2026-66296.html | related |
| https://osv.dev/vulnerability/EEF-CVE-2026-66296 | related |
| https://github.com/lud/oaskit/commit/b70c6b2eaf0b… | patch |
Impacted products
Date Public
2026-07-05 00:00
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"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"tags": [
"Patch"
],
"url": "https://github.com/lud/oaskit/commit/b70c6b2eaf0b11bdd0bbb21b8a87dbb3d46918a1"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"tags": [
"Exploit",
"Vendor Advisory"
],
"url": "https://github.com/lud/oaskit/security/advisories/GHSA-h7xw-x8wr-xpcc"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"tags": [
"Patch",
"Third Party Advisory"
],
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-66296"
},
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"tags": [
"Exploit",
"Vendor Advisory"
],
"url": "https://github.com/lud/oaskit/security/advisories/GHSA-h7xw-x8wr-xpcc"
}
],
"sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"vulnStatus": "Analyzed",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-79"
}
],
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"type": "Secondary"
}
]
}
},
"vulnrichment": {
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-66296",
"options": [
{
"Exploitation": "poc"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-08-03T19:50:03.665445Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-08-03T19:50:23.782Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"references": [
{
"tags": [
"exploit"
],
"url": "https://github.com/lud/oaskit/security/advisories/GHSA-h7xw-x8wr-xpcc"
}
],
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"collectionURL": "https://repo.hex.pm",
"cpes": [
"cpe:2.3:a:lud:oaskit:*:*:*:*:*:elixir:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"Elixir.Oaskit.ErrorHandler.Default"
],
"packageName": "oaskit",
"packageURL": "pkg:hex/oaskit",
"product": "oaskit",
"programFiles": [
"lib/oaskit/error_handler/default.ex"
],
"programRoutines": [
{
"name": "\u0027Elixir.Oaskit.ErrorHandler.Default\u0027:format_reason/4"
},
{
"name": "\u0027Elixir.Oaskit.ErrorHandler.Default\u0027:reason_to_html/1"
}
],
"repo": "https://github.com/lud/oaskit",
"vendor": "lud",
"versions": [
{
"lessThan": "0.14.1",
"status": "affected",
"version": "0.1.0",
"versionType": "semver"
}
]
},
{
"collectionURL": "https://github.com",
"cpes": [
"cpe:2.3:a:lud:oaskit:*:*:*:*:*:elixir:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"Elixir.Oaskit.ErrorHandler.Default"
],
"packageName": "lud/oaskit",
"packageURL": "pkg:github/lud/oaskit",
"product": "oaskit",
"programFiles": [
"lib/oaskit/error_handler/default.ex"
],
"programRoutines": [
{
"name": "\u0027Elixir.Oaskit.ErrorHandler.Default\u0027:format_reason/4"
},
{
"name": "\u0027Elixir.Oaskit.ErrorHandler.Default\u0027:reason_to_html/1"
}
],
"repo": "https://github.com/lud/oaskit",
"vendor": "lud",
"versions": [
{
"lessThan": "b70c6b2eaf0b11bdd0bbb21b8a87dbb3d46918a1",
"status": "affected",
"version": "552de8ca0ff60617bea58bcafa451892d61a161c",
"versionType": "git"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:a:lud:oaskit:*:*:*:*:*:elixir:*:*",
"versionEndExcluding": "0.14.1",
"versionStartIncluding": "0.1.0",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
],
"operator": "AND"
}
],
"credits": [
{
"lang": "en",
"type": "finder",
"value": "Ludovic Dem"
},
{
"lang": "en",
"type": "remediation developer",
"value": "Ludovic Dem"
},
{
"lang": "en",
"type": "analyst",
"value": "Jonatan M\u00e4nnchen / EEF"
}
],
"datePublic": "2026-07-05T00:00:00.000Z",
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eImproper Neutralization of Input During Web Page Generation (XSS) vulnerability in lud oaskit allows reflected cross-site scripting via the default HTML error handler.\u003c/p\u003e\n\u003cp\u003e\u003ccode\u003eOaskit.ErrorHandler.Default.format_reason/4\u003c/code\u003e and \u003ccode\u003eOaskit.ErrorHandler.Default.reason_to_html/1\u003c/code\u003e in \u003ccode\u003elib/oaskit/error_handler/default.ex\u003c/code\u003e render request-validation failures as an HTML page whenever the request\u0027s \u003ccode\u003eAccept\u003c/code\u003e header contains \u003ccode\u003ehtml\u003c/code\u003e, interpolating request-controlled strings into that page without HTML escaping. The unescaped values are object keys taken from a request body or from an object or \u003ccode\u003edeepObject\u003c/code\u003e query parameter, which appear in the JSON Schema error\u0027s instance path when a schema rejects them (for example under \u003ccode\u003eadditionalProperties: false\u003c/code\u003e), and the raw \u003ccode\u003eContent-Type\u003c/code\u003e header, reflected in unsupported-media-type errors when it fails to parse.\u003c/p\u003e\n\u003cp\u003eBecause browsers send \u003ccode\u003eAccept: text/html\u003c/code\u003e on ordinary top-level navigation, a crafted GET link is sufficient to trigger the error page; no form submission, custom \u003ccode\u003eContent-Type\u003c/code\u003e, or attacker-controlled script on the victim\u0027s side is required. A payload such as \u003ccode\u003efilter[\u0026lt;/code\u0026gt;\u0026lt;/h2\u0026gt;\u0026lt;script\u0026gt;alert(document.domain)\u0026lt;/script\u0026gt;]=x\u003c/code\u003e terminates the enclosing markup and the injected script executes in the origin of the application using oaskit, giving it access to that origin\u0027s cookies, session, and same-origin responses.\u003c/p\u003e\n\u003cp\u003eBoth HTML error rendering and the vulnerable handler are enabled by default: \u003ccode\u003eOaskit.Plugs.ValidateRequest\u003c/code\u003e defaults \u003ccode\u003e:html_errors\u003c/code\u003e to \u003ccode\u003etrue\u003c/code\u003e and \u003ccode\u003e:error_handler\u003c/code\u003e to \u003ccode\u003eOaskit.ErrorHandler.Default\u003c/code\u003e, so applications following the documented usage are affected without any opt-in.\u003c/p\u003e\n\u003cp\u003eThis issue affects oaskit: from 0.1.0 before 0.14.1.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"value": "Improper Neutralization of Input During Web Page Generation (XSS) vulnerability in lud oaskit allows reflected cross-site scripting via the default HTML error handler.\n\n`Oaskit.ErrorHandler.Default.format_reason/4` and `Oaskit.ErrorHandler.Default.reason_to_html/1` in `lib/oaskit/error_handler/default.ex` render request-validation failures as an HTML page whenever the request\u0027s `Accept` header contains `html`, interpolating request-controlled strings into that page without HTML escaping. The unescaped values are object keys taken from a request body or from an object or `deepObject` query parameter, which appear in the JSON Schema error\u0027s instance path when a schema rejects them (for example under `additionalProperties: false`), and the raw `Content-Type` header, reflected in unsupported-media-type errors when it fails to parse.\n\nBecause browsers send `Accept: text/html` on ordinary top-level navigation, a crafted GET link is sufficient to trigger the error page; no form submission, custom `Content-Type`, or attacker-controlled script on the victim\u0027s side is required. A payload such as `filter[\u003c/code\u003e\u003c/h2\u003e\u003cscript\u003ealert(document.domain)\u003c/script\u003e]=x` terminates the enclosing markup and the injected script executes in the origin of the application using oaskit, giving it access to that origin\u0027s cookies, session, and same-origin responses.\n\nBoth HTML error rendering and the vulnerable handler are enabled by default: `Oaskit.Plugs.ValidateRequest` defaults `:html_errors` to `true` and `:error_handler` to `Oaskit.ErrorHandler.Default`, so applications following the documented usage are affected without any opt-in.\n\nThis issue affects oaskit: from 0.1.0 before 0.14.1."
}
],
"value": "Improper Neutralization of Input During Web Page Generation (XSS) vulnerability in lud oaskit allows reflected cross-site scripting via the default HTML error handler.\n\nOaskit.ErrorHandler.Default.format_reason/4 and Oaskit.ErrorHandler.Default.reason_to_html/1 in lib/oaskit/error_handler/default.ex render request-validation failures as an HTML page whenever the request\u0027s Accept header contains html, interpolating request-controlled strings into that page without HTML escaping. The unescaped values are object keys taken from a request body or from an object or deepObject query parameter, which appear in the JSON Schema error\u0027s instance path when a schema rejects them (for example under additionalProperties: false), and the raw Content-Type header, reflected in unsupported-media-type errors when it fails to parse.\n\nBecause browsers send Accept: text/html on ordinary top-level navigation, a crafted GET link is sufficient to trigger the error page; no form submission, custom Content-Type, or attacker-controlled script on the victim\u0027s side is required. A payload such as filter[\u003c/code\u003e\u003c/h2\u003e\u003cscript\u003ealert(document.domain)\u003c/script\u003e]=x terminates the enclosing markup and the injected script executes in the origin of the application using oaskit, giving it access to that origin\u0027s cookies, session, and same-origin responses.\n\nBoth HTML error rendering and the vulnerable handler are enabled by default: Oaskit.Plugs.ValidateRequest defaults :html_errors to true and :error_handler to Oaskit.ErrorHandler.Default, so applications following the documented usage are affected without any opt-in.\n\nThis issue affects oaskit: from 0.1.0 before 0.14.1."
}
],
"impacts": [
{
"capecId": "CAPEC-591",
"descriptions": [
{
"lang": "en",
"value": "CAPEC-591 Reflected XSS"
}
]
}
],
"metrics": [
{
"cvssV4_0": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"baseScore": 5.1,
"baseSeverity": "MEDIUM",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "LOW",
"subIntegrityImpact": "LOW",
"userInteraction": "ACTIVE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "NONE",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-79",
"description": "CWE-79 Improper Neutralization of Input During Web Page Generation (\u0027Cross-site Scripting\u0027)",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-03T19:04:30.556Z",
"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"shortName": "EEF"
},
"references": [
{
"tags": [
"vendor-advisory",
"related"
],
"url": "https://github.com/lud/oaskit/security/advisories/GHSA-h7xw-x8wr-xpcc"
},
{
"tags": [
"related"
],
"url": "https://cna.erlef.org/cves/CVE-2026-66296.html"
},
{
"tags": [
"related"
],
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-66296"
},
{
"tags": [
"patch"
],
"url": "https://github.com/lud/oaskit/commit/b70c6b2eaf0b11bdd0bbb21b8a87dbb3d46918a1"
}
],
"source": {
"discovery": "INTERNAL"
},
"title": "Reflected XSS in oaskit\u0027s default HTML error handler",
"workarounds": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eDisable HTML error rendering so that validation failures are returned as JSON only:\u003c/p\u003e\n\u003cpre\u003e\u003ccode class=\"language-elixir\"\u003eplug Oaskit.Plugs.ValidateRequest, html_errors: false\n\u003c/code\u003e\u003c/pre\u003e\n\u003cp\u003eThis prevents the vulnerable HTML page from being rendered at all, on any oaskit version. Alternatively, configure a custom \u003ccode\u003e:error_handler\u003c/code\u003e that does not emit HTML built from request-derived values.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"value": "Disable HTML error rendering so that validation failures are returned as JSON only:\n\n```elixir\nplug Oaskit.Plugs.ValidateRequest, html_errors: false\n```\n\nThis prevents the vulnerable HTML page from being rendered at all, on any oaskit version. Alternatively, configure a custom `:error_handler` that does not emit HTML built from request-derived values."
}
],
"value": "Disable HTML error rendering so that validation failures are returned as JSON only:\n\nplug Oaskit.Plugs.ValidateRequest, html_errors: false\n\nThis prevents the vulnerable HTML page from being rendered at all, on any oaskit version. Alternatively, configure a custom :error_handler that does not emit HTML built from request-derived values."
}
]
}
},
"cveMetadata": {
"assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"assignerShortName": "EEF",
"cveId": "CVE-2026-66296",
"datePublished": "2026-08-03T19:04:30.556Z",
"dateReserved": "2026-07-24T14:10:01.114Z",
"dateUpdated": "2026-08-03T19:50:27.860Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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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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