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Fencer Intel
medium 5.3

CVE-2026-121373 json

Symfony: HtmlSanitizer MetaRefreshAttributeSanitizer Matches Only a Narrow Subset of the Browser Refresh Grammar (Incomplete Fix for CVE-2026-48761)

published 5d ago modified 3d ago also EUVD-2026-116909

cvss
5.3
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 41%
public exploits
0
none known

Summary

The Symfony HtmlSanitizer component MetaRefreshAttributeSanitizer, introduced to fix CVE-2026-48761, sanitizes the refresh URL of content attributes of meta tags using a regular expression that is too narrow, allowing sanitization to be bypassed, and resulting in potential URL redirection to untrusted sites 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 shared declarative refresh steps in the WHATWG HTML Standard require a broader approach: the separator after the time may be ASCII whitespace alone, with no ; or ,, and the url= keyword is optional. Directives the browser honours, but the regular expression misses are returned unchanged, so the attacker URL skips UrlSanitizer entirely and both allowLinkSchemes and allowLinkHosts are defeated for the refresh navigation.

This is reachable under any configuration that allows meta with http-equiv and content, including the documented allowStaticElements() preset.

Patch / fix

  • symfony Debian 13 6.4.50+dfsg-0+deb13u1
  • symfony Debian 14 7.4.23+dfsg-1

debian advisories DEBIAN-CVE-2026-121373

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CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
5d ago

Exploit prediction

0.48% chance of exploitation in the next 30 days, higher than 41% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 4.0 5.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
CNA 4.0 5.3 CVSS:4.0/AV:N/AC:L/AT:N/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

Affected products

  • sensiolabs symfony

Classification

Weakness
  • CWE-186 Overly Restrictive Regular Expression
  • CWE-601 URL Redirection to Untrusted Site

References

Sources

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