EUVD-2026-38344
GHSA-w88c-7765-q5gg
Severity by source
AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
AC:H for inherent race condition timing requirement; C:L added over official C:N to reflect 'Information Disclosure' tag - misrouted responses may leak sensitive data.
Primary rating from Vendor (CNA).
CVSS VectorNVD
Lifecycle Timeline
4Description PRE-NVD
AnalysisAI
Response queue poisoning in Node.js http.Agent allows network-accessible attackers to corrupt the HTTP keep-alive connection pool via a TOCTOU race condition, causing responses to be delivered to the wrong request handler. Affected is Node.js v26.x prior to v26.3.1, as disclosed in the June 2026 security release. Exploitation requires high attack complexity due to the race window, and no public exploit has been identified at time of analysis; this is rated Low severity (CVSS 3.7) by the Node.js team.
Technical ContextAI
The vulnerability resides in Node.js's built-in http.Agent, which manages HTTP/1.1 keep-alive connection pooling and request multiplexing over persistent TCP sockets. CWE-367 (Time-of-check Time-of-use / TOCTOU race condition) is the root cause: the agent checks the state of the response queue at one point in time, but by the time it acts on that state, concurrent request activity has altered the queue, allowing a response frame to be dispatched to the wrong pending request callback. This is structurally similar to HTTP response desynchronization but arises from an internal race rather than protocol-level smuggling. The fix is attributed to Matteo Collina and was shipped in llhttp 9.4.2 (bundled in v26.3.1), as evidenced by the concurrent dep update commit 110840f2c7.
RemediationAI
Upgrade to Node.js v26.3.1 or later, which contains the patched http.Agent response queue logic and the updated llhttp 9.4.2 dependency. The vendor advisory is at https://nodejs.org/en/blog/vulnerability/june-2026-security-releases and the release notes at https://github.com/nodejs/node/releases/tag/v26.3.1. If an immediate upgrade is not feasible, a targeted compensating control is to disable HTTP keep-alive in http.Agent by setting keepAlive: false when constructing agent instances - this eliminates connection reuse and closes the race window entirely, at the cost of one TCP handshake per request (latency and throughput regression under high request volumes). Alternatively, limiting concurrency of outbound HTTP requests sharing a single Agent instance reduces the probability of the race condition being triggered. Generic network-layer controls will not mitigate this issue as it is an internal Node.js runtime race.
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Same technique Information Disclosure
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External POC / Exploit Code
Leaving vuln.today