CVE-2026-67354: guzzlehttp/guzzle before 7.15.1 URI Fragment Disclosure via Referer

Severity: medium (CVSS 5.9 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-01 · updated 2026-10-08
Weakness: CWE-201

Description

guzzlehttp/guzzle versions before 7.15.1 contain an information disclosure vulnerability in RedirectMiddleware. When the optional allow_redirects.referer setting is enabled, the middleware copies the URI fragment (the portion after '#') from the referring request into the generated Referer header when following a same-scheme redirect (e.g., HTTPS to HTTPS). An attacker who controls the redirect destination can read this fragment from the incoming Referer header, potentially disclosing one-time login secrets, access tokens, state values, or other sensitive client data to a server never meant to receive it. The referer setting is disabled by default. Fixed in 7.15.1, which strips the fragment before generating the Referer value.

Affected products

Packagist Guzzlehttp/Guzzle: before 7.15.1; 4.0.0, 4.0.0-rc.1, 4.0.0-rc.2, 4.0.1, 4.0.2, 4.1.0 (+168) — fixed in 7.15.1
guzzle: before 7.15.1 — fixed in 7.15.1

How to fix

Upgrade to a fixed version: Packagist Guzzlehttp/Guzzle 7.15.1; guzzle 7.15.1. Check the vendor advisory for mitigations.

References

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