{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-126075", "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa", "state": "PUBLISHED", "assignerShortName": "GitHub_M", "dateReserved": "2026-11-10T17:07:43.284Z", "datePublished": "2026-11-10T20:50:44.522Z", "dateUpdated": "2026-11-10T20:50:44.522Z"}, "containers": {"cna": {"title": "Active Support: Possible XSS vulnerability in Active Support MessagePack serializer", "problemTypes": [{"descriptions": [{"cweId": "CWE-79", "lang": "en", "description": "CWE-79: Improper Neutralization of Input During Web Page Generation", "type": "CWE"}]}], "metrics": [{"cvssV3_1": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 4.7, "baseSeverity": "MEDIUM", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "privilegesRequired": "NONE", "scope": "CHANGED", "userInteraction": "REQUIRED", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N", "version": "3.1"}}], "references": [{"name": "https://github.com/rails/rails/security/advisories/GHSA-2w9f-fxwj-w2qf", "tags": ["x_refsource_CONFIRM"], "url": "https://github.com/rails/rails/security/advisories/GHSA-2w9f-fxwj-w2qf"}, {"name": "https://github.com/rails/rails/commit/4ca090665976e6fbc471c38689b399f84b43cdc7", "tags": ["x_refsource_MISC"], "url": "https://github.com/rails/rails/commit/4ca090665976e6fbc471c38689b399f84b43cdc7"}, {"name": "https://github.com/rails/rails/releases/tag/v8.1.4.1", "tags": ["x_refsource_MISC"], "url": "https://github.com/rails/rails/releases/tag/v8.1.4.1"}], "affected": [{"vendor": "rails", "product": "rails", "versions": [{"version": ">= 8.1, < 8.1.4.1", "status": "affected"}]}], "providerMetadata": {"orgId": "a0819718-46f1-4df5-94e2-005712e83aaa", "shortName": "GitHub_M", "dateUpdated": "2026-11-10T20:50:44.522Z"}, "descriptions": [{"lang": "en", "value": "Active Support is a collection of utility classes and standard library extensions used by Rails and other Ruby projects. From 8.1 until 8.1.4.1, ActiveSupport::MessagePack serializes an ActiveSupport::SafeBuffer as its bytes alone and deserializes it as a new SafeBuffer, so a buffer that is no longer html_safe? (for example, one mutated in place with gsub!) is restored as html_safe. If such a buffer holds untrusted input and is stored through a MessagePack serializer, rendering it after it is loaded bypasses ERB auto-escaping, possibly leading to XSS. Applications on Rails 8.1 are affected if they use a MessagePack serializer, such as config.action_dispatch.cookies_serializer = :message_pack or :message_pack_allow_marshal, or serializer: :message_pack for Rails.cache, ActiveSupport::MessageVerifier or ActiveSupport::MessageEncryptor, and store a SafeBuffer that was mutated in place with untrusted input. Rails 8.0 and earlier do not serialize SafeBuffer with MessagePack and are not affected. This issue is fixed in version 8.1.4.1."}], "source": {"advisory": "GHSA-2w9f-fxwj-w2qf", "discovery": "UNKNOWN"}}}}

{}

{"affected": [{"affectedData": [{"product": "rails", "vendor": "rails", "versions": [{"status": "affected", "version": ">= 8.1, < 8.1.4.1"}]}], "source": "[email protected]"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "Active Support is a collection of utility classes and standard library extensions used by Rails and other Ruby projects. From 8.1 until 8.1.4.1, ActiveSupport::MessagePack serializes an ActiveSupport::SafeBuffer as its bytes alone and deserializes it as a new SafeBuffer, so a buffer that is no longer html_safe? (for example, one mutated in place with gsub!) is restored as html_safe. If such a buffer holds untrusted input and is stored through a MessagePack serializer, rendering it after it is loaded bypasses ERB auto-escaping, possibly leading to XSS. Applications on Rails 8.1 are affected if they use a MessagePack serializer, such as config.action_dispatch.cookies_serializer = :message_pack or :message_pack_allow_marshal, or serializer: :message_pack for Rails.cache, ActiveSupport::MessageVerifier or ActiveSupport::MessageEncryptor, and store a SafeBuffer that was mutated in place with untrusted input. Rails 8.0 and earlier do not serialize SafeBuffer with MessagePack and are not affected. This issue is fixed in version 8.1.4.1."}], "id": "CVE-2026-126075", "lastModified": "2026-11-10T21:19:25.880", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 4.7, "baseSeverity": "MEDIUM", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "privilegesRequired": "NONE", "scope": "CHANGED", "userInteraction": "REQUIRED", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N", "version": "3.1"}, "exploitabilityScore": 1.6, "impactScore": 2.7, "source": "[email protected]", "type": "Secondary"}]}, "published": "2026-11-10T21:19:25.880", "references": [{"source": "[email protected]", "url": "https://github.com/rails/rails/commit/4ca090665976e6fbc471c38689b399f84b43cdc7"}, {"source": "[email protected]", "url": "https://github.com/rails/rails/releases/tag/v8.1.4.1"}, {"source": "[email protected]", "url": "https://github.com/rails/rails/security/advisories/GHSA-2w9f-fxwj-w2qf"}], "sourceIdentifier": "[email protected]", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-79"}], "source": "[email protected]", "type": "Primary"}]}

{}

{}