GHSA-wm3w-8rrp-j577 is a medium-severity (CVSS 5.9) CWE-201 vulnerability in guzzlehttp/guzzle. O3 Security confirms whether GHSA-wm3w-8rrp-j577 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Guzzle: Host-only cookie scope is not preserved
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 GHSA-wm3w-8rrp-j577.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-wm3w-8rrp-j577 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 373,366 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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
In affected versions, CookieJar does not preserve whether a response cookie was set without a Domain attribute or with an empty one. A cookie without Domain is host-only and must be returned only to the exact host that set it. Under current cookie processing rules, an empty Domain value is also host-only. Guzzle instead stores the request host in the cookie's Domain field and later applies ordinary domain matching, as though the server had supplied a valid domain. For example, a host-only sid=secret cookie set by example.com can subsequently be sent to child.example.com. FileCookieJar and SessionCookieJar also persist the request host without recording the host-only state, so reloading a jar preserves the widened scope.
An attacker who controls or can observe a child host can therefore receive cookies that were intended only for its parent host. Depending on the cookie, this can disclose session identifiers, authorization tokens, or other sensitive state. Exploitation requires the application to enable Guzzle's cookie support, reuse the same built-in cookie jar, receive a host-only cookie from a parent host, and later make a matching request to a less-trusted child host. The cookie's other restrictions still apply. Its path must match, a Secure cookie is sent only over a secure connection, and an expired cookie is not sent.
Applications that do not use Guzzle's cookie support are not affected. Applications are also not affected by this disclosure if they use a separate jar for every host or trust boundary, never request a less-trusted subdomain with the same jar, or only store cookies carrying a valid, non-empty Domain attribute. The incorrect behavior occurs between an otherwise valid parent host and its subdomains.
Patches
The issue is patched in 7.15.1 and later. Starting in that release, Guzzle records whether a response cookie is host-only and matches it only against the exact host. The host-only flag is part of cookie identity for replacement and response-driven deletion. Cookies carrying a valid, non-empty Domain attribute retain their existing domain-matching behavior. A host-only cookie can coexist with an explicit-domain cookie having the same name, domain string, and path.
The built-in persistent jars now write a boolean HostOnly marker for every stored cookie record. They reject records where that marker is missing or is not a boolean, and validate all records before changing the live jar. Persisted cookie records written by an older version are therefore rejected rather than silently interpreted with an unsafe scope. Loading non-empty file or session data written without this marker throws a RuntimeException until the data is deleted, regenerated, or correctly annotated. Versions before 7.15.1 are affected.
Workarounds
If you cannot upgrade immediately, do not reuse one CookieJar instance across parent and child hosts with different trust levels. Use a separate cookie jar for each host or trust boundary, disable cookie handling for requests to less-trusted hosts, or avoid making those requests through a client configured with a shared jar. In particular, avoid new Client(['cookies' => true]) for a client that may contact both a trusted parent host and less-trusted subdomains, because that option creates one jar for the whole client.
When upgrading, delete or rotate existing FileCookieJar and SessionCookieJar data that contains cookie records written without a HostOnly marker. Records may instead be annotated manually only when the original presence or absence of the cookie's Domain attribute is known. The stored domain string is not sufficient to infer it safely.
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | guzzlehttp/guzzle | all versions | 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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update guzzlehttp/guzzle to 7.15.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-wm3w-8rrp-j577 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.
How O3 protects you
O3 pinpoints whether GHSA-wm3w-8rrp-j577 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-wm3w-8rrp-j577. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-wm3w-8rrp-j577 in your dependencies?
O3 detects GHSA-wm3w-8rrp-j577 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.