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CVE-2026-118517

Symfony: HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URLs Without a Well-Formed Authority (Incomplete Fix for CVE-2026-45066)

No known exploitation. EPSS puts it in the 18th percentile. Fixed versions are out.

CVSS 3.14.3MediumEPSS percentile18th0.3% chance in 30 daysCISA KEVNot listedNo confirmed exploitation
No public exploit knownFix1 product3 fixed builds listed below
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Published Updated Sources: CVE.org, NVD

NVD CVE.org

What to do

Find your product and version, then upgrade to the build on the right.

  • Sensiolabs SymfonyAffected: ≥ 6.1.0, < 6.4.50Upgrade to: 6.4.50Affected: ≥ 7.0.0, < 7.4.23Upgrade to: 7.4.23Affected: ≥ 8.0.0, < 8.1.11Upgrade to: 8.1.11Stated by: CVE record

Versions as the sources state them. Full version matrix after sign-in

What it is

From the CVE record

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.

In plain language

No plain-language summary for this CVE yet.

Exploitation

Where each signal puts this CVE on the scale from published to confirmed exploited.

EPSS18th
CISA KEV

Not in the catalog. CISA has not confirmed exploitation.

Public exploits

No public exploit or proof of concept found in the sources we track.

EPSS

0.3% chance of exploitation activity in the next 30 days, which ranks it in the 18th percentile of scored CVEs.

Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.

Lifecycle

4 events over 1 day, from the signal feeds we watch.

  1. Record updated
  2. Publishedweakness classified, record updated

Affected products

Technical detail

CVSS 3.1 vector

Open in the CVSS calculator

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Scored 4.3 by NVD.

How it is reached

  • Attack Vector NetworkExploitable remotely over the network without any special conditions
  • Attack Complexity LowNo special conditions — the attack can be reliably reproduced
  • Privileges Required NoneNo authentication required — anyone can exploit this
  • User Interaction RequiredA user must click a link, open a file, or perform some action

Scope

  • Scope UnchangedImpact is limited to the vulnerable component itself

Impact if exploited

  • Confidentiality NoneNo confidentiality impact
  • Integrity LowData modification is possible but limited in scope or consequence
  • Availability NoneNo availability impact

Weaknesses

Sources

References in the record

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