Summary
AsyncHttpClient stores cookie for an unrelated domain (cookie tossing) via ThreadSafeCookieStore
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.
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.
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.
CVE-2026-55688 has a CVSS score of 4.0 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.0.11, 2.16.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Fixed in 3.0.11 and 2.16.0
Frequently Asked Questions
- What is CVE-2026-55688? CVE-2026-55688 is a medium-severity security vulnerability in org.asynchttpclient:async-http-client (maven), affecting versions >= 3.0.0.Beta1, < 3.0.11. It is fixed in 3.0.11, 2.16.0.
- How severe is CVE-2026-55688? CVE-2026-55688 has a CVSS score of 4.0 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of org.asynchttpclient:async-http-client are affected by CVE-2026-55688? org.asynchttpclient:async-http-client (maven) versions >= 3.0.0.Beta1, < 3.0.11 is affected.
- Is there a fix for CVE-2026-55688? Yes. CVE-2026-55688 is fixed in 3.0.11, 2.16.0. Upgrade to this version or later.
- Is CVE-2026-55688 exploitable, and should I be worried? Whether CVE-2026-55688 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-55688 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-55688?
- Upgrade
org.asynchttpclient:async-http-clientto 3.0.11 or later - Upgrade
org.asynchttpclient:async-http-clientto 2.16.0 or later
- Upgrade