guzzlehttp/psr7 security advisory

CVE-2026-59882: Guzzlehttp/psr7: Host Confusion via Weak URI Host Validation

CVE-2026-59882 is a medium-severity security vulnerability in the PHP package guzzlehttp/psr7 (CVSS 6.5), published 8 July 2026. It is fixed in 2.12.3; earlier versions are affected. It can be exploited without an account.

medium 6.5 published 2026-07-08 · updated 2026-10-25

Affected versions: < 2.12.3
Fixed in: 2.12.3
Newest release: 3.2.0
Severity: Medium · CVSS 6.5
Type: Security issue
CWE-436
Exploited in the wild: Not on the CISA KEV list
checked 2026-11-04

Is your guzzlehttp/psr7 version affected?

Run composer show guzzlehttp/psr7 in your project, then enter the version. We check it against this and every other known guzzlehttp/psr7 advisory.

Who can exploit CVE-2026-59882

Access: No account. Anyone who can send a request to an app that uses the affected code.

CVSS vector (scored by NVD): CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Your app is only exposed if it uses the affected part of guzzlehttp/psr7. The advisory below says which part that is. If you are not sure, upgrade anyway: it costs less than finding out.

How to fix CVE-2026-59882 in guzzlehttp/psr7

Find the installed version: composer show guzzlehttp/psr7. If you never required it yourself, composer why guzzlehttp/psr7 shows which package pulls it in.
Update it: composer update guzzlehttp/psr7 --with-all-dependencies. You need 2.12.3 or newer.
If Composer will not go that high, your composer.json constraint is holding it back. Widen it (for example "guzzlehttp/psr7": "^2.12.3" if you can take that version), or upgrade the package that requires it.
Run composer audit. It reads the same advisory data and should no longer list CVE-2026-59882.
Commit composer.lock and deploy it. On the server, run composer install --no-dev from the lock file, not composer update.

If you cannot upgrade yet

General hardening for this kind of issue while the upgrade waits. None of it replaces the fix.

If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-59882 advisory

guzzlehttp/psr7 is a PSR-7 HTTP message library implementation in PHP. Prior to 2.12.3, Uri::assertValidHost() does not reject URI host components containing authority delimiters, embedded ports, or malformed IPv6 brackets, allowing Uri::getHost() to disagree with the URI authority used for security or routing decisions. This issue is fixed in version 2.12.3.

Description from the CVE record, published by GitHub (the CVE Numbering Authority), via the NVD entry for CVE-2026-59882. Advisory title: “guzzlehttp/psr7: Host Confusion via Weak URI Host Validation”.

References

GitHub advisory GHSA-c2w2-prh8-qm98 github.com
Fix commit ddd64f1 github.com
Pull request #811 github.com
Release 2.12.3 github.com

Other guzzlehttp/psr7 advisories

medium CVE-2026-55766: CRLF injection in HTTP start-line serialization 2026-06-18
medium CVE-2026-48998: Host confusion via authority reinterpretation 2026-05-25
medium CVE-2026-49214: CRLF injection via URI host component 2026-05-25
medium CVE-2023-29197: Improper header validation 2023-04-17
medium CVE-2022-24775: Inproper parsing of HTTP headers 2022-03-20

Need help patching or upgrading? Laskyr does PHP and Laravel security fixes and upgrades. Tell us what you run and we reply with a plan and a price.

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Where this data comes from

Affected and fixed versions: the Packagist security advisories API (GitHub Advisory Database and FriendsOfPHP), the same data composer audit uses. Synced 2026-11-03.
Description, score, weakness and references: NIST National Vulnerability Database (NVD), checked 2026-11-04. This product uses data from the NVD API but is not endorsed or certified by the NVD.
Exploited-in-the-wild status: the CISA Known Exploited Vulnerabilities catalog, checked 2026-11-04.
Compiled by Daniel Lasek at Laskyr from the sources above. The summary, “who can exploit it”, “how to fix it” and hardening sections are our plain-English reading of the record and are generated from it. The quoted description is the record's own text. Spot an error? Tell us.