CVE-2026-67354 — guzzle
Fix: guzzle/guzzle#3901CVE-2026-67354 is a CWE-201 vulnerability in guzzlehttp/guzzle. A fix is available for guzzlehttp/guzzle — see the affected versions and patch details below.
guzzlehttp/guzzle before 7.15.1 URI Fragment Disclosure via Referer
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-67354.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
Real-World Exposure
guzzlehttp/guzzleReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Impact
When the optional referer redirect setting is enabled, affected versions of RedirectMiddleware can copy the fragment from the referring request URI into a generated Referer header. A URI fragment is the part after #. It is handled locally by the client and is not part of the HTTP request target, so the server handling the original request does not receive it. A generated Referer tells the redirect destination which URI led to the request. Guzzle correctly removes user information from that value, but retains the fragment when it follows a redirect to the same scheme, such as HTTPS to HTTPS. For example, an initial URI ending in #secret is sent without the fragment, but the redirect destination can receive a Referer ending in #secret. This behavior affects both the cURL and stream handlers.
An attacker who controls the redirect destination can read the fragment from the incoming header, including through request logs or application code. If the fragment contains a one-time login secret, access token, state value, or other private client data, it is disclosed to a server that was never meant to receive it. Exploitation requires the application to enable allow_redirects.referer, make a request to a URI with a sensitive fragment, and follow a same-scheme redirect to a less-trusted destination.
The referer setting is disabled by default. Applications that leave it disabled, do not put sensitive data in URI fragments, do not follow redirects, or only redirect within the same trust boundary are not affected. Guzzle already omits the generated header when the scheme changes. This issue is limited to the fragment's inclusion. Reducing the path and query on cross-origin redirects is a separate privacy policy question.
Patches
The issue is patched in 7.15.1 and later. Starting in that release, Guzzle removes both user information and the fragment before generating a redirect Referer value. Other redirect behavior does not change. Guzzle retains the referring path and query, and continues to omit the header when the scheme changes. Versions before 7.15.1 are affected when the optional referer setting is enabled.
Workarounds
If you cannot upgrade immediately, leave automatic Referer generation disabled. It is off by default. If redirect options are configured explicitly, ensure that referer is false:
$client->request('GET', $uri, [
'allow_redirects' => ['referer' => false],
]);
Alternatively, disable automatic redirects and follow trusted destinations manually, or remove the fragment from the request URI before sending a request that may redirect. Do not rely on the fact that fragments are absent from the initial HTTP request target, because the affected middleware can reintroduce them in the generated header.
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | guzzlehttp/guzzle | all versions | 7.15.1composer require guzzlehttp/guzzle:^7.15.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for guzzlehttp/guzzle, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update guzzlehttp/guzzle to 7.15.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-67354 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Community packages in Fedora and EPEL that bundle guzzlehttp/guzzle (nextcloud, roundcubemail) already ship patched versions (7.15.2 and 7.15.3 respectively) that include the fix for this vulnerability, and are therefore not affected. Additionally, exploitation requires the non-default allow_redirects.referer setting…
Upgrade guzzlehttp/guzzle to version 7.15.1 or later.Source: Red Hat security advisory for CVE-2026-67354 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-67354 in your dependencies?
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