guzzlehttp/psr7: Malformed URI Hosts Can Fool Host Checks

Published as "guzzlehttp/psr7: Host Confusion via Weak URI Host Validation"

medium Guzzle · Last reviewed Nov 2, 2026

CVE: CVE-2026-59882
GHSA: GHSA-c2w2-prh8-qm98
Packagist: PKSA-vznr-tgp9-fd7d
Reported: Jul 21, 2026

Lets an attacker get past host allowlists or SSRF checks in apps that build a psr7 Uri from user input and trust getHost().

Affected and fixed versions

In guzzlehttp/psr7. Find the row for the version you run, and update to the release next to it.

If you run	Update to	Support
Up to 2.12.2	2.12.3	Supported

Upgrade

Run the line for the branch you are on.

composer require guzzlehttp/psr7:^2.12.3

What this means

guzzlehttp/psr7 accepted URI hosts that contained characters such as @, / or #, a port, or broken IPv6 brackets. When that happens, Uri::getHost() can name a different host from the one a request really goes to. An app that trusts getHost() to decide where a request may go can be tricked into sending it somewhere else.

That can lead to host allowlist bypasses, server-side request forgery (getting your server to make requests on an attacker's behalf), or Host header confusion.

Who is affected

Apps on guzzlehttp/psr7 before 2.12.3 that build a Uri, or call Uri::withHost(), with host data an attacker controls, and then use getHost() for a security or routing decision. The psr7 advisory also lists apps that parse, forward or re-send raw HTTP messages from untrusted sources. Guzzle uses psr7, so apps that build Guzzle request URLs from untrusted host input are affected the same way. If every host you put in a Uri is already trusted and well formed, you aren't affected.

What to do

Update guzzlehttp/psr7 to 2.12.3. The fix rejects these malformed hosts. Until you can update, check host values yourself before building a Uri, and don't treat getHost() as a trust boundary.

Reported by GrahamCampbell.

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: guzzlehttp/psr7: Malformed URI Hosts Can Fool Host Checks (CVE-2026-59882, GHSA-c2w2-prh8-qm98)
Details: https://phpnews.net/security/guzzle/ghsa-c2w2-prh8-qm98

Affected versions, as Composer constraints:
- guzzlehttp/psr7: <2.12.3

Fixed releases on branches that still get security fixes:
- Up to 2.12.2: update to 2.12.3

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/guzzle/ghsa-c2w2-prh8-qm98 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 Guzzle advisories