VulnerabilityPublished 1 Jul 2026Updated 6 Aug 2026

CVE-2026-55688: AsyncHttpClient async-http-client · Sensitive Cookie with Improper SameSite Attribute

Affects AsyncHttpClient async-http-clientSource CVE Database V5

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Not known to be exploited · CVSS 4.0 Medium : upgrade to 3.0.11 or 2.16.0 when convenient.

Data as of 12 Nov 2026, 23:24 UTC

CVSS 3.1 base score

4.0Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 26% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.0.11, 2.16.0

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Changed
Confidentiality: None
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 1 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade async-http-client to 3.0.11 or 2.16.0; org.asynchttpclient/async-http-client to 2.16.0.

Affected software

Product	Affected	Fixed in
AsyncHttpClientasync-http-client	Affected >=3.0.0.Beta1 <3.0.11	Fixed in 3.0.11
AsyncHttpClientasync-http-client	Affected >=2.0.0 <2.16.0	Fixed in 2.16.0
Mavenorg.asynchttpclient/async-http-client`pkg:maven/org.asynchttpclient/async-http-client`Other threats	Affected 2.0.0 <2.16.0	Fixed in 2.16.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade AsyncHttpClient to version 2.16.0 or later, or 3.0.11 or later, where this vulnerability is fixed. There is no indication of alternative mitigations or temporary fixes. Patch status is not explicitly confirmed in the vendor advisory, but the description states the issue is fixed in these versions.

Description

The AsyncHttpClient (AHC) library allows Java applications to easily execute HTTP requests and asynchronously process HTTP responses. In versions from 2.0.0 prior to 2.16.0 and from 3.0.0.Beta1 prior to 3.0.11, 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, leading to a cookie tossing / cookie injection issue. 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. Applications that use a single AsyncHttpClient instance - and thus the default, shared CookieStore - to reach both an attacker-influenced host and a trusted host are impacted. This issue has been fixed in versions 2.16.0 and 3.0.11.

Impact

An attacker controlling a host that the client connects to can inject cookies scoped to unrelated domains into the client's cookie store. This may cause the client to send attacker-injected cookies to trusted domains, potentially leading to session confusion or other unintended behaviors. The CVSS score is 4.0 (medium severity) with network attack vector, high attack complexity, no privileges required, no user interaction, and impact limited to integrity.

Summary

The AsyncHttpClient library suffers from a cookie tossing/cookie injection vulnerability due to ThreadSafeCookieStore storing cookies without verifying the domain authorization of the responding host. This flaw allows an attacker-controlled host to set cookies for unrelated domains, which the client will send on later requests, potentially leading to unintended cookie sharing across domains. The vulnerability affects versions from 2.0.0 up to but not including 2.16.0 and from 3.0.0.Beta1 up to but not including 3.0.11. The issue is resolved in versions 2.16.0 and 3.0.11.

CWE-1275Sensitive Cookie with Improper SameSite Attribute (opens in a new tab)
Variant weaknessLikelihood of exploit: MediumOWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The SameSite attribute for sensitive cookies is not set, or an insecure value is used.
Implementation
Set the SameSite attribute of a sensitive cookie to "Lax" or "Strict". This instructs the browser to apply this cookie only to same-domain requests, which provides a good Defense in Depth against CSRF attacks.
OWASP Cheat Sheets
Cross-Site Request Forgery Prevention (opens in a new tab)
Session Management (opens in a new tab)
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V3.4.3 (opens in a new tab)
V1.14.1 (opens in a new tab)
V1.4.4 (opens in a new tab)
Attack patterns
Cross Site Request Forgery (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 7 Aug 2026, 13:26 UTC

WeaknessesCWE-1275

Technical details

References

Community reviews

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