Guzzle: Oddly Written Hosts Can Slip Past Host-Based Checks

Published as "Guzzle: Noncanonical host can bypass host-based checks"

high Guzzle · Last reviewed Nov 1, 2026

CVE: CVE-2026-69246
GHSA: GHSA-v5mv-p594-2x33
Packagist: PKSA-gcrk-3vtt-1r14
Reported: Aug 3, 2026

Lets an attacker reach hosts an app meant to block, such as loopback, when the app builds Guzzle request URLs from user input and checks the host first.

Affected and fixed versions

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

If you run	Update to	Support
8.0.0	8.0.1	Supported
Up to 7.15.1	7.15.2	Supported

Upgrade

Run the line for the branch you are on.

composer require guzzlehttp/guzzle:^8.0.1
composer require guzzlehttp/guzzle:^7.15.2

What this means

An attacker who can influence a URL your app fetches with Guzzle can reach a host your app meant to block, such as the server itself, and read the response. This is a kind of server-side request forgery (SSRF): getting your server to make requests on the attacker's behalf.

Guzzle checked the host as written, but the network layer could read an oddly written host as a different one. The same mismatch could also send Authorization and Cookie headers, or proxy decisions, the wrong way.

Who is affected

Apps on guzzlehttp/guzzle before 7.15.2, or 8.0.0, that build a request URL from untrusted input and check the host before sending it. The Guzzle advisory says denylists, private address checks and IP checks are the ones at risk. An exact allowlist of host names usually fails safe. Apps that only fetch URLs they build themselves aren't affected.

What to do

Update to 7.15.2, or to 8.0.1 on 8.x. The fix rejects hosts with escapes and other odd characters before any request goes out. If you can't update yet, the advisory shows how to check the host yourself, on every redirect.

Guzzle says it doesn't offer SSRF protection, and numeric spellings like 127.1 are still accepted after the fix. Where the destination matters, resolve the host and check the addresses it points to.

Reported by bilguunbicktivism.

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: Guzzle: Oddly Written Hosts Can Slip Past Host-Based Checks (CVE-2026-69246, GHSA-v5mv-p594-2x33)
Details: https://phpnews.net/security/guzzle/ghsa-v5mv-p594-2x33

Affected versions, as Composer constraints:
- guzzlehttp/guzzle: >=8.0.0,<8.0.1|<7.15.2

Fixed releases on branches that still get security fixes:
- 8.0.0: update to 8.0.1
- Up to 7.15.1: update to 7.15.2

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-v5mv-p594-2x33 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