FKIE_CVE-2026-121949

Vulnerability from fkie_nvd - Published: 2026-11-05 18:17 - Updated: 2026-11-05 20:17
Severity
5.4 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Summary
The Symfony HtmlSanitizer component does not apply the media URL policy to the srcset and imagesrcset attributes, allowing values that point to hosts or schemes not permitted by allowMediaSchemes() or allowMediaHosts() to bypass it, so that browsers load images from disallowed hosts in Symfony versions 6.1.x prior to 6.4.50, 7.x prior to 7.4.23, and 8.x prior to 8.1.11.The srcset attribute on img and source elements and the imagesrcset attribute on link elements are allowed by the sanitizer, but their URL candidates are never validated, so their values are kept verbatim while the same URL in src is dropped. The fixes for CVE-2026-45753 and CVE-2026-48761 extended the same attribute list but did not cover these two attributes. For example, with allowMediaSchemes(['https']) and allowMediaHosts(['trusted.example']), <img srcset="https://evil.example/a.png 1x"> survives sanitization, and the browser fetches the selected candidate as it would fetch src. Candidates with a scheme forbidden by the configuration, such as http, are kept as well. Any application that sanitizes untrusted HTML and relies on the media schemes and hosts allowlists to restrict where images can be loaded from is affected. A single crafted value is enough to make the browser of a user viewing the sanitized content send a request to an attacker-controlled host, which can be used to track viewers or log their IP addresses. No authentication is needed if the application accepts HTML from unauthenticated users.
References
596c5446-0ce5-4ba2-aa66-48b3b757a647https://github.com/symfony/symfony/commit/50e7a38a8f088601c09669b9d267c9c0228884e1
596c5446-0ce5-4ba2-aa66-48b3b757a647https://github.com/symfony/symfony/security/advisories/GHSA-q8jq-xrf4-v5j8
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "collectionURL": "https://packagist.org/packages/symfony/html-sanitizer",
          "defaultStatus": "unaffected",
          "modules": [
            "Symfony\\Component\\HtmlSanitizer"
          ],
          "packageName": "symfony/html-sanitizer",
          "product": "symfony",
          "repo": "https://github.com/symfony/html-sanitizer",
          "vendor": "sensiolabs",
          "versions": [
            {
              "lessThan": "6.4.50",
              "status": "affected",
              "version": "6.1.0",
              "versionType": "git"
            },
            {
              "lessThan": "7.4.23",
              "status": "affected",
              "version": "7.0.0",
              "versionType": "git"
            },
            {
              "lessThan": "8.1.11",
              "status": "affected",
              "version": "8.0.0",
              "versionType": "git"
            }
          ]
        }
      ],
      "source": "596c5446-0ce5-4ba2-aa66-48b3b757a647"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "The Symfony HtmlSanitizer component does not apply the media URL policy to the\u00a0srcset\u00a0and\u00a0imagesrcset\u00a0attributes, allowing values that point to hosts or schemes not permitted by\u00a0allowMediaSchemes()\u00a0or\u00a0allowMediaHosts()\u00a0to bypass it, so that browsers load images from disallowed hosts in Symfony versions 6.1.x prior to 6.4.50, 7.x prior to 7.4.23, and 8.x prior to 8.1.11.The\u00a0srcset\u00a0attribute on\u00a0img\u00a0and\u00a0source\u00a0elements and the\u00a0imagesrcset\u00a0attribute on\u00a0link\u00a0elements are allowed by the sanitizer, but their URL candidates are never validated, so their values are kept verbatim while the same URL in\u00a0src\u00a0is dropped. The fixes for CVE-2026-45753 and CVE-2026-48761 extended the same attribute list but did not cover these two attributes. For example, with\u00a0allowMediaSchemes([\u0027https\u0027]) and allowMediaHosts([\u0027trusted.example\u0027]), \u003cimg srcset=\"https://evil.example/a.png 1x\"\u003e survives sanitization, and the browser fetches the selected candidate as it would fetch src. Candidates with a scheme forbidden by the configuration, such as http, are kept as well.\nAny application that sanitizes untrusted HTML and relies on the media schemes and hosts allowlists to restrict where images can be loaded from is affected. A single crafted value is enough to make the browser of a user viewing the sanitized content send a request to an attacker-controlled host, which can be used to track viewers or log their IP addresses.\u00a0No authentication is needed if the application accepts HTML from unauthenticated users."
    }
  ],
  "id": "CVE-2026-121949",
  "lastModified": "2026-11-05T20:17:48.910",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 5.4,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 2.5,
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "type": "Secondary"
      }
    ],
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 2.3,
          "baseSeverity": "LOW",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "LOW",
          "subIntegrityImpact": "LOW",
          "userInteraction": "PASSIVE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "NONE",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "596c5446-0ce5-4ba2-aa66-48b3b757a647",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-121949",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-11-05T19:59:10.426339Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-11-05T18:17:07.480",
  "references": [
    {
      "source": "596c5446-0ce5-4ba2-aa66-48b3b757a647",
      "url": "https://github.com/symfony/symfony/commit/50e7a38a8f088601c09669b9d267c9c0228884e1"
    },
    {
      "source": "596c5446-0ce5-4ba2-aa66-48b3b757a647",
      "url": "https://github.com/symfony/symfony/security/advisories/GHSA-q8jq-xrf4-v5j8"
    }
  ],
  "sourceIdentifier": "596c5446-0ce5-4ba2-aa66-48b3b757a647",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-184"
        },
        {
          "lang": "en",
          "value": "CWE-1023"
        }
      ],
      "source": "596c5446-0ce5-4ba2-aa66-48b3b757a647",
      "type": "Secondary"
    }
  ]
}



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