GHSA-35p6-xmwp-9g52 — low GitHub Advisory (CVE-2026-6733) in npm/undici

Description

Impact

Undici's HTTP/1.1 client is vulnerable to response queue poisoning on reused keep-alive sockets. An attacker-controlled upstream server can inject an unsolicited HTTP/1.1 response onto an idle socket after a request completes. When the client dispatches the next request on that socket, it associates the injected response with the new request, causing responses to be delivered to the wrong requests.

This requires an attacker-controlled or compromised upstream HTTP/1.1 server and keep-alive connection reuse.

Patches

Upgrade to undici v6.27.0, v7.28.0 or v8.5.0.

Workarounds

Disable keep-alive connection reuse by setting keepAliveTimeout: 0 on the Client or Pool.

Basic information

Type: reviewed
Severity: low
Advisory on GitHub: Open advisory ↗
Repository advisory: Open repository advisory ↗
Source code: Browse source ↗
Published (advisory): 2026-06-19 14:19:13 UTC
Updated: 2026-06-19 14:19:15 UTC
GitHub reviewed: 2026-06-19 14:19:13 UTC
NVD published: 2026-06-17

Score	Percentile
0.18%	7.37%

CVSS Scores

Base score	Version	Severity	Vector
3.7	3.1	—	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:H) Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:N) Service keeps running; no real outage angle.

Identifiers

Type	Value
GHSA	GHSA-35p6-xmwp-9g52 ↗
CVE	CVE-2026-6733 ↗

CWEs

CWE id	Name
CWE-367	Time-of-check Time-of-use (TOCTOU) Race Condition

Credits

mcollina (remediation_developer)
UlisesGascon (remediation_verifier)

Affected packages (3)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem	Package	Vulnerable range	First patched	Vulnerable functions
npm	undici	< 6.27.0	6.27.0	—
npm	undici	>= 7.0.0, < 7.28.0	7.28.0	—
npm	undici	>= 8.0.0, < 8.5.0	8.5.0	—

undici vulnerable to HTTP response queue poisoning via keep-alive socket reuse