CVE-2026-55688 is a medium-severity (CVSS 4) CWE-1275 vulnerability in org.asynchttpclient:async-http-client. A fix is available for org.asynchttpclient:async-http-client — see the affected versions and patch details below.
AsyncHttpClient: Cookie stored for an unrelated domain (cookie tossing) via ThreadSafeCookieStore
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-2026-55688.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-55688 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
org.asynchttpclient:async-http-client☕org.asynchttpclient:async-http-clientReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Impact
A cookie tossing / cookie injection issue (CWE-1275). ThreadSafeCookieStore stored a cookie under the value of its Domain attribute without verifying that the responding host is allowed to set a cookie for that domain (RFC 6265 §5.3 step 6). A host the client connects to can therefore plant a cookie scoped to an unrelated domain, and the client will then send that cookie on later requests to that domain.
Who is Impacted
Applications that use a single AsyncHttpClient instance - and thus the default, shared CookieStore - to reach both an attacker-influenced host and a trusted host. Typical exposure: crawlers, link-preview / webhook fetchers, SSRF-style "fetch this URL" features, multi-backend aggregators, or following redirects to an attacker-controlled host. The attacker can write a cookie the client presents to the victim host (session fixation, overwriting a session id / CSRF-token cookie); they cannot read the victim host's cookies. Applications that talk only to a fixed trusted backend, or that disable/scope the cookie store, are not exposed.
Patches
Fixed in 3.0.11 and 2.16.0
Workarounds
- Disable the cookie store (setCookieStore(null)) when cookies are not needed; or
- Use a separate AsyncHttpClient (separate cookie store) per trust domain so an attacker-influenced host and a trusted host never share a jar
- Supply a custom CookieStore whose add(Uri, Cookie) rejects cookies whose Domain is not domain-matched by the request host.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.asynchttpclient:async-http-client | ≥ 3.0.0.Beta1&&< 3.0.11 | 3.0.11org.asynchttpclient:async-http-client:3.0.11 |
| ☕Maven | org.asynchttpclient:async-http-client | ≥ 2.0.0&&< 2.16.0 | 2.16.0org.asynchttpclient:async-http-client:2.16.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.asynchttpclient:async-http-client, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.asynchttpclient:async-http-client to 3.0.11 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55688 is resolved across your whole dependency graph.
Workarounds
Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.
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.
This Moderate impact flaw in the AsyncHttpClient library, affecting Red Hat Enterprise Application Platform, allows a malicious server to inject cookies for unrelated domains. This occurs when an application uses a shared AsyncHttpClient instance to communicate with both untrusted and trusted external services,…
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.Source: Red Hat security advisory for CVE-2026-55688 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-55688 in your dependencies?
Find it across Maven, including transitive dependencies.