CVE-2026-121373

5.3 MEDIUM 0.5% exploit odds Fix listed XSS Web app

What it is

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.

At a glance

Exploitability: Can be exploited over the network without logging in, but needs a user to act. Limited direct impact.
Exploit odds: 0.5% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-11-03 11:38 UTC ReservedThe CVE id was reserved by its CNA
2026-11-04 13:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-11-06 21:40 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.5% in the next 30 days (EPSS).
Severity: 5.3 MEDIUM (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-11-04 13:17 UTC
Last modified: 2026-11-06 21:40 UTC
Exploit probability: 0.5% · EPSS, next 30 days
Weakness: CWE-186
Record status: Awaiting Analysis

Attack profile CVSS 4.0 · 5.3

Attack vector: Network
Complexity: Low
Attack requirements: None
Privileges needed: None
User interaction: Passive
Confidentiality: None
Integrity: None
Availability: None

Raw vector

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

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-121373.md and follow it. Check whether this project is affected by CVE-2026-121373. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record