CVE-2026-118517 (GCVE-0-2026-118517)

Vulnerability from cvelistv5 – Published: 2026-11-05 16:26 – Updated: 2026-11-05 16:52
VLAI
Title
Symfony: HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URLs Without a Well-Formed Authority (Incomplete Fix for CVE-2026-45066)
Summary
The Symfony HtmlSanitizer component UrlSanitizer parses URLs differently from browsers, allowing the allowLinkHosts() and allowMediaHosts() checks to be bypassed for URLs without a well-formed authority, resulting in untrusted hosts being referenced in sanitized output 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. UrlSanitizer parses URLs with league/uri, which follows RFC 3986, while browsers follow the WHATWG URL standard. For URLs without a well-formed authority, such as http:evil.example, ///evil.example, or https://://evil.example/ the sanitizer finds no host, whereas browsers resolve them to evil.example. The guard added for CVE-2026-45066 missed the zero-slash form, and the host 0 was also skipped because PHP treats it as falsy. This is exploitable when a host allow-list is combined with allowRelativeLinks(true) or allowRelativeMedias(true). The default configuration is not affected.
Severity
2.3 (Low)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
4.3 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
SSVC
Exploitation: poc Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-11-05 16:49 UTC
CWE
  • CWE-184 - Incomplete List of Disallowed Inputs
  • CWE-436 - Interpretation Conflict
Assigner
Checkmarx CNA under the mitre root
CNA scorecard B 88/100 over 23 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
sensiolabs symfony Affected: 6.1.0 , < 6.4.50 (git)
Affected: 7.0.0 , < 7.4.23 (git)
Affected: 8.0.0 , < 8.1.11 (git)
    cpe:2.3:a:sensiolabs:symfony:*:*:*:*:*:*:*:*
    cpe:2.3:a:sensiolabs:symfony:*:*:*:*:*:*:*:*
    cpe:2.3:a:sensiolabs:symfony:*:*:*:*:*:*:*:*
Create a notification for this product.
Credits
Nicolas Grekas Ilia Alshanetsky
Show details on NVD website
To clipboard 

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                      "versionEndExcluding": "8.1.11",
                      "versionStartIncluding": "8.0.0",
                      "vulnerable": true
                    }
                  ],
                  "negate": false,
                  "operator": "OR"
                }
              ],
              "operator": "OR"
            }
          ],
          "credits": [
            {
              "lang": "en",
              "type": "remediation developer",
              "value": "Nicolas Grekas"
            },
            {
              "lang": "en",
              "type": "reporter",
              "value": "Ilia Alshanetsky"
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "supportingMedia": [
                {
                  "base64": false,
                  "type": "text/html",
                  "value": "\u003cp\u003eThe Symfony HtmlSanitizer component \u003ccode\u003eUrlSanitizer\u003c/code\u003e\u0026nbsp;parses URLs differently from browsers, allowing\u0026nbsp;\u003cspan\u003ethe \u003c/span\u003e\u003ccode\u003eallowLinkHosts()\u003c/code\u003e\u003cspan\u003e and \u003c/span\u003e\u003ccode\u003eallowMediaHosts()\u003c/code\u003e\u003cspan\u003e checks to be bypassed for URLs without a well-formed authority,\u003c/span\u003e\u003cspan\u003e\u0026nbsp;\u003c/span\u003eresulting in untrusted hosts being referenced in sanitized output\u003cspan\u003e\u0026nbsp;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.\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003ccode\u003eUrlSanitizer\u003c/code\u003e\u003cspan\u003e parses URLs with \u003c/span\u003e\u003ccode\u003eleague/uri\u003c/code\u003e\u003cspan\u003e, which follows RFC 3986, while browsers follow the WHATWG URL standard.\u0026nbsp;\u003c/span\u003eFor URLs without a well-formed authority, such as \u003ccode\u003ehttp:evil.example\u003c/code\u003e, \u003ccode\u003e///evil.example\u003c/code\u003e, or \u003ccode\u003ehttps://://evil.example/\u0026nbsp;\u003c/code\u003et\u003cspan\u003ehe sanitizer finds no host, whereas browsers resolve them to \u003c/span\u003e\u003ccode\u003eevil.example\u003c/code\u003e\u003cspan\u003e. The guard added for CVE-2026-45066 missed the zero-slash form, and the host \u003c/span\u003e\u003ccode\u003e0\u003c/code\u003e\u003cspan\u003e was also skipped because PHP treats it as falsy.\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cspan\u003eThis is exploitable when a host allow-list is combined with \u003c/span\u003e\u003ccode\u003eallowRelativeLinks(true)\u003c/code\u003e\u003cspan\u003e or \u003c/span\u003e\u003ccode\u003eallowRelativeMedias(true)\u003c/code\u003e\u003cspan\u003e. The default configuration is not affected.\u003c/span\u003e\u003c/p\u003e"
                }
              ],
              "value": "The Symfony HtmlSanitizer component UrlSanitizer\u00a0parses URLs differently from browsers, allowing\u00a0the allowLinkHosts() and allowMediaHosts() checks to be bypassed for URLs without a well-formed authority,\u00a0resulting in untrusted hosts being referenced in sanitized output\u00a0in 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.\n\n\n\nUrlSanitizer parses URLs with league/uri, which follows RFC 3986, while browsers follow the WHATWG URL standard.\u00a0For URLs without a well-formed authority, such as http:evil.example, ///evil.example, or https://://evil.example/\u00a0the sanitizer finds no host, whereas browsers resolve them to evil.example. The guard added for CVE-2026-45066 missed the zero-slash form, and the host 0 was also skipped because PHP treats it as falsy.\n\n\n\nThis is exploitable when a host allow-list is combined with allowRelativeLinks(true) or allowRelativeMedias(true). The default configuration is not affected."
            }
          ],
          "metrics": [
            {
              "cvssV4_0": {
                "Automatable": "NOT_DEFINED",
                "Recovery": "NOT_DEFINED",
                "Safety": "NOT_DEFINED",
                "attackComplexity": "LOW",
                "attackRequirements": "PRESENT",
                "attackVector": "NETWORK",
                "baseScore": 2.3,
                "baseSeverity": "LOW",
                "exploitMaturity": "NOT_DEFINED",
                "privilegesRequired": "NONE",
                "providerUrgency": "NOT_DEFINED",
                "subAvailabilityImpact": "NONE",
                "subConfidentialityImpact": "NONE",
                "subIntegrityImpact": "NONE",
                "userInteraction": "PASSIVE",
                "valueDensity": "NOT_DEFINED",
                "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N",
                "version": "4.0",
                "vulnAvailabilityImpact": "NONE",
                "vulnConfidentialityImpact": "NONE",
                "vulnIntegrityImpact": "LOW",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
              },
              "format": "CVSS",
              "scenarios": [
                {
                  "lang": "en",
                  "value": "GENERAL"
                }
              ]
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-184",
                  "description": "CWE-184 Incomplete List of Disallowed Inputs",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            },
            {
              "descriptions": [
                {
                  "cweId": "CWE-436",
                  "description": "CWE-436 Interpretation Conflict",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-11-05T16:26:52.166Z",
            "orgId": "596c5446-0ce5-4ba2-aa66-48b3b757a647",
            "shortName": "Checkmarx"
          },
          "references": [
            {
              "tags": [
                "third-party-advisory"
              ],
              "url": "https://github.com/symfony/symfony/security/advisories/GHSA-c76g-9c4c-gxrw"
            },
            {
              "tags": [
                "patch"
              ],
              "url": "https://github.com/symfony/symfony/commit/f2f47d2eef6c2552c6c5c24953caa94f7901cb43"
            }
          ],
          "source": {
            "advisory": "GHSA-c76g-9c4c-gxrw",
            "discovery": "UNKNOWN"
          },
          "title": "Symfony: HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URLs Without a Well-Formed Authority (Incomplete Fix for CVE-2026-45066)",
          "x_generator": {
            "engine": "Vulnogram 1.0.5"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "596c5446-0ce5-4ba2-aa66-48b3b757a647",
        "assignerShortName": "Checkmarx",
        "cveId": "CVE-2026-118517",
        "datePublished": "2026-11-05T16:26:52.166Z",
        "dateReserved": "2026-10-28T14:33:36.992Z",
        "dateUpdated": "2026-11-05T16:52:28.063Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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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

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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.
Vulnerability timeline

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Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

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