CVE-2026-121949

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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(['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.\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.", "supportingMedia": [{"type": "text/html", "base64": false, "value": "The Symfony HtmlSanitizer component does not apply the media URL policy to the&nbsp;<code>srcset</code>&nbsp;and&nbsp;<code>imagesrcset</code>&nbsp;attributes, allowing values that point to hosts or schemes not permitted by&nbsp;<code>allowMediaSchemes()</code>&nbsp;or&nbsp;<code>allowMediaHosts()</code>&nbsp;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.<div>The&nbsp;<code>srcset</code>&nbsp;attribute on&nbsp;<code>img</code>&nbsp;and&nbsp;<code>source</code>&nbsp;elements and the&nbsp;<code>imagesrcset</code>&nbsp;attribute on&nbsp;<code>link</code>&nbsp;elements are allowed by the sanitizer, but their URL candidates are never validated, so their values are kept verbatim while the same URL in&nbsp;<code>src</code>&nbsp;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&nbsp;<code>allowMediaSchemes(['https'])</code> and <code>allowMediaHosts(['trusted.example'])</code>, <code>&lt;img srcset=\"https://evil.example/a.png 1x\"&gt;</code> survives sanitization, and the browser fetches the selected candidate as it would fetch <code>src</code>. Candidates with a scheme forbidden by the configuration, such as <code>http</code>, are kept as well.<br>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. 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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(['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.\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.", "supportingMedia": [{"type": "text/html", "value": "The Symfony HtmlSanitizer component does not apply the media URL policy to the&nbsp;<code>srcset</code>&nbsp;and&nbsp;<code>imagesrcset</code>&nbsp;attributes, allowing values that point to hosts or schemes not permitted by&nbsp;<code>allowMediaSchemes()</code>&nbsp;or&nbsp;<code>allowMediaHosts()</code>&nbsp;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.<div>The&nbsp;<code>srcset</code>&nbsp;attribute on&nbsp;<code>img</code>&nbsp;and&nbsp;<code>source</code>&nbsp;elements and the&nbsp;<code>imagesrcset</code>&nbsp;attribute on&nbsp;<code>link</code>&nbsp;elements are allowed by the sanitizer, but their URL candidates are never validated, so their values are kept verbatim while the same URL in&nbsp;<code>src</code>&nbsp;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&nbsp;<code>allowMediaSchemes(['https'])</code> and <code>allowMediaHosts(['trusted.example'])</code>, <code>&lt;img srcset=\"https://evil.example/a.png 1x\"&gt;</code> survives sanitization, and the browser fetches the selected candidate as it would fetch <code>src</code>. Candidates with a scheme forbidden by the configuration, such as <code>http</code>, are kept as well.<br>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.&nbsp;No authentication is needed if the application accepts HTML from unauthenticated users.</div>", "base64": false}]}], "problemTypes": [{"descriptions": [{"lang": "en", "type": "CWE", "cweId": "CWE-184", "description": "CWE-184 Incomplete list of disallowed inputs"}]}, {"descriptions": [{"lang": "en", "type": "CWE", "cweId": "CWE-1023", "description": "CWE-1023 Incomplete Comparison with Missing Factors"}]}], "cpeApplicability": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:sensiolabs:symfony:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "6.4.50", "versionStartIncluding": "6.1.0"}, {"criteria": "cpe:2.3:a:sensiolabs:symfony:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "7.4.23", "versionStartIncluding": "7.0.0"}, {"criteria": "cpe:2.3:a:sensiolabs:symfony:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "8.1.11", "versionStartIncluding": "8.0.0"}], "operator": "OR"}], "operator": "OR"}], "providerMetadata": {"orgId": "596c5446-0ce5-4ba2-aa66-48b3b757a647", "shortName": "Checkmarx", "dateUpdated": "2026-11-05T17:46:04.672Z"}}}, "cveMetadata": {"cveId": "CVE-2026-121949", "state": "PUBLISHED", "dateUpdated": "2026-11-05T19:59:59.269Z", "dateReserved": "2026-11-04T12:43:13.943Z", "assignerOrgId": "596c5446-0ce5-4ba2-aa66-48b3b757a647", "datePublished": "2026-11-05T17:46:04.672Z", "assignerShortName": "Checkmarx"}, "dataVersion": "5.2"}

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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": "2026-11-06T21:40:43.450", "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": "Awaiting Analysis", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-184"}, {"lang": "en", "value": "CWE-1023"}], "source": "596c5446-0ce5-4ba2-aa66-48b3b757a647", "type": "Secondary"}]}

{"bugzilla": {"description": "symfony/html-sanitizer: symfony/html-sanitizer: Information disclosure via media policy bypass in srcset attributes", "id": "2567531", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2567531"}, "csaw": false, "cvss3": {"cvss3_base_score": "5.4", "cvss3_scoring_vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N", "status": "draft"}, "cwe": "CWE-184", "details": ["A flaw was found in symfony/html-sanitizer. The HTML sanitizer fails to enforce configured media host and URL scheme restrictions on srcset and imagesrcset attributes. A remote attacker could exploit this vulnerability by submitting crafted HTML with image sources pointing to unauthorized domains. When another user views the sanitized content, their browser connects to the disallowed server, potentially allowing the attacker to track users or log their IP addresses."], "mitigation": {"lang": "en:us", "value": "Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability."}, "name": "CVE-2026-121949", "public_date": "2026-11-05T17:46:04Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-121949\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-121949\nhttps://github.com/symfony/symfony/commit/50e7a38a8f088601c09669b9d267c9c0228884e1\nhttps://github.com/symfony/symfony/security/advisories/GHSA-q8jq-xrf4-v5j8"], "statement": "This vulnerability is rated as Moderate severity because exploitation requires victim interaction and the resulting impact is confined to low-level information disclosure, such as client IP tracking, rather than arbitrary code execution or data corruption. In typical Red Hat environments, the Symfony HtmlSanitizer component is only exposed when applications explicitly define media domain or scheme restrictions while sanitizing untrusted markup. Without a user actively rendering the manipulated HTML output in a browser, the unverified image sources cannot trigger outbound network connections.", "threat_severity": "Moderate"}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[6.1.0,6.4.50)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[7.0.0,7.4.23)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[8.0.0,8.1.11)"}}], "enrichment": {"confidence": 95.0, "confidence_source": "inferred", "scores": [{"score": 95.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "symfony", "source": "cna", "vendor": "sensiolabs"}, "product": "symfony", "vendor": "sensiolabs"}], "created": "2026-11-05T20:00:08.734917+00:00", "updated": "2026-11-05T20:30:16.094336+00:00", "vendors": ["sensiolabs", "sensiolabs$PRODUCT$symfony"]}