guzzlehttp/psr7 security advisory

CVE-2026-48998: Host confusion via authority reinterpretation in guzzlehttp/psr7

CVE-2026-48998 is a medium-severity SSRF vulnerability in the PHP package guzzlehttp/psr7 (CVSS 5.3), published 11 June 2026. It is fixed in 2.10.2; earlier versions are affected. It can be exploited without an account.

medium 5.3 published 2026-06-11 · updated 2026-10-26

Affected versions: < 2.10.2
Fixed in: 2.10.2
Newest release: 3.2.0
Severity: Medium · CVSS 5.3
Type: Server-side request forgery (SSRF)
CWE-20, CWE-918
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-2026-48998

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

CVSS vector (scored by GitHub): CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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-2026-48998 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 2.10.2 or newer.
If Composer will not go that high, your composer.json constraint is holding it back. Widen it (for example "guzzlehttp/psr7": "^2.10.2" 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-2026-48998.
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

The advisory gives this workaround:

Some workarounds are available.

General hardening for SSRF issues while the upgrade waits. None of it replaces the fix.

Block outbound requests from the app server to private ranges and cloud metadata (169.254.169.254) at the firewall.
Do not pass user-supplied URLs to the affected feature.
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-48998 advisory

guzzlehttp/psr7 is a PSR-7 HTTP message library implementation in PHP. Versions prior to 2.10.2 contain improper Host header validation when parsing raw HTTP request messages and when deriving a server request URI from server variables. An attacker can provide a malformed Host header containing URI authority delimiters, such as `trusted.example@evil.example`. When the Host value is used to construct a URI, the malformed value can be reinterpreted as URI userinfo and host. This can cause the PSR-7 request URI host to differ from the original Host header value. Applications are affected if they parse attacker-controlled raw HTTP requests with `GuzzleHttp\Psr7\Message::parseRequest()` or the legacy 1.x `GuzzleHttp\Psr7\parse_request()` function, or if they build server requests from attacker-controlled server variables, then rely on the resulting URI host for routing, allow-list checks, or forwarding decisions. In affected forwarding or gateway scenarios, this may cause requests or credentials to be sent to an unintended host. The issue is patched in `2.10.2`. `1.x` is end-of-life and will not receive a patch. Some workarounds are available. Validate the `Host` header as `uri-host [ ":" port ]` before calling `Message::parseRequest()` or legacy `parse_request()` on untrusted HTTP request data, or before deriving routing and forwarding decisions from a parsed request URI. Reject Host values containing userinfo, path, query, or fragment delimiters.

Description from the CVE record, published by GitHub (the CVE Numbering Authority), via the NVD entry for CVE-2026-48998. Advisory title: “Host confusion via authority reinterpretation”.

References

GitHub security advisory GHSA-34xg-wgjx-8xph github.com

Other guzzlehttp/psr7 advisories

medium CVE-2026-59882: Guzzlehttp/psr7: Host Confusion via Weak URI Host Validation 2026-07-21
medium CVE-2026-55766: CRLF injection in HTTP start-line serialization 2026-06-18
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

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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.