Symfony HtmlSanitizer: Meta Refresh URLs Slip Past Link Checks

Published as "HtmlSanitizer MetaRefreshAttributeSanitizer Matches Only a Narrow Subset of the Browser Refresh Grammar: Incomplete Fix for CVE-2026-48761"

medium Symfony Symfony components · Last reviewed Nov 10, 2026

CVE: CVE-2026-121373
GHSA: None
Packagist: PKSA-4z5q-y2w8-bwqq
Reported: Nov 4, 2026

Lets meta refresh tags send visitors to blocked hosts or javascript: URLs in apps that allow meta refresh through HtmlSanitizer.

Affected and fixed versions

In 2 packages: symfony/html-sanitizer and symfony/symfony. Find the row for the version you run, and update to the release next to it.

If you run	Update to	Support
8.1.0 – 8.1.10	8.1.11	Supported
7.4.0 – 7.4.22	7.4.23	Supported
6.4.0 – 6.4.49	6.4.50	Supported

Show 8 older branches, no longer supported

8.0.0 – 8.0.x	8.1.11
7.0.0 – 7.0.x	7.4.23
7.1.0 – 7.1.x	7.4.23
7.2.0 – 7.2.x	7.4.23
7.3.0 – 7.3.x	7.4.23
6.1.0 – 6.1.x	6.4.50
6.2.0 – 6.2.x	6.4.50
6.3.0 – 6.3.x	6.4.50

Upgrade

Run the line for the branch you are on. 1 other package listed above is affected too; update it the same way.

composer require symfony/html-sanitizer:^8.1.11
composer require symfony/html-sanitizer:^7.4.23
composer require symfony/html-sanitizer:^6.4.50

What this means

Content that HtmlSanitizer cleans can still include a <meta> refresh tag that sends visitors to a host you didn't allow, or to a javascript: URL. The sanitizer only checked refresh URLs written in one narrow format, and browsers accept several more.

This is an incomplete fix for CVE-2026-48761.

Who is affected

Apps on symfony/html-sanitizer (also part of symfony/symfony) whose HtmlSanitizerConfig allows the meta element with http-equiv and content. The Symfony advisory says that includes the allowStaticElements() preset. allowLinkHosts() and allowLinkSchemes() don't apply to these refresh URLs. Configurations that don't allow meta aren't affected.

What to do

Update to 6.4.50, 7.4.23 or 8.1.11. If you're on 8.0, update to 8.1.11. The fix reads refresh values the way browsers do, and drops the attribute when it can't make the URL safe.

One side effect: any <meta content> value that starts with a digit or a full stop, such as a description like "10 tips", is now dropped too. The sanitizer can't tell which meta element it belongs to.

Reported by Ilia Alshanetsky.

Check your app with an agent

Paste this into a coding agent that can read your project, such as Claude Code, Codex or Amp. It checks your composer.lock against the versions above and tells you what to update, without changing anything.

Check whether the PHP project you have access to is affected by this security advisory, and tell me what to update. Do a read-only check: don't edit files, don't run composer update or composer require, and don't try to reproduce the flaw.

Advisory: Symfony HtmlSanitizer: Meta Refresh URLs Slip Past Link Checks (CVE-2026-121373)
Details: https://phpnews.net/security/symfony/pksa-zt69-bd63-2wsb

Affected versions, as Composer constraints:
- symfony/html-sanitizer, symfony/symfony: >=6.1.0,<6.2.0|>=6.2.0,<6.3.0|>=6.3.0,<6.4.0|>=6.4.0,<6.4.50|>=7.0.0,<7.1.0|>=7.1.0,<7.2.0|>=7.2.0,<7.3.0|>=7.3.0,<7.4.0|>=7.4.0,<7.4.23|>=8.0.0,<8.1.0|>=8.1.0,<8.1.11

Fixed releases on branches that still get security fixes:
- 8.1.0 – 8.1.10: update to 8.1.11
- 7.4.0 – 7.4.22: update to 7.4.23
- 6.4.0 – 6.4.49: update to 6.4.50

1. Find every composer.lock in the project outside vendor/ (a monorepo can have one per app) and read the installed version of each package above. Packages installed as dependencies of other packages count too.
2. Compare each installed version with its constraint: "|" separates alternative ranges, and "," means both bounds apply.
3. For each affected install, read "What this means" at https://phpnews.net/security/symfony/pksa-zt69-bd63-2wsb and check whether the project meets the conditions it describes (a feature in use, a config value, a driver). Say which conditions you could check and which you couldn't.
4. Report a table: lock file | package | installed version | affected (yes, no or unknown) | conditions met (yes, no or unknown) | update to | evidence. For each affected package, give the command that would fix it, without running it: composer update <package> --with-dependencies when it is only installed as a dependency of another package, or composer require with the fixed version when composer.json requires it directly. If the installed version is on a branch with no fixed release listed, say it needs a move to a newer branch.

Sources

← All Symfony advisories