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undici vulnerable to cross-user cookie disclosure via Set-Cookie caching in shared caches

Moderate severity GitHub Reviewed Published Sep 4, 2026 in nodejs/undici • Updated Sep 29, 2026

Package

npm undici (npm)

Affected versions

>= 7.0.0, < 7.29.1
>= 8.0.0, < 8.10.2

Patched versions

7.29.1
8.10.2

Description

Impact

undici's interceptors.cache() does not handle Set-Cookie in the cache path. In shared-cache mode (type: 'shared', the default), a cacheable response (for example Cache-Control: public, max-age=...) carrying a Set-Cookie header is stored, and the stored Set-Cookie is re-served to a later caller that hits the same cache key. This exposes one user's cookie to another caller and lets an untrusted upstream inject cookies into cached responses served to all subsequent callers, violating RFC 6265 section 7.2 (a shared cache must not store cookies). Applications using the shared cache interceptor against untrusted or multi-user upstreams are affected. Private caches (type: 'private') are not affected.

Patches

Upgrade to 7.29.1 or 8.10.2. In shared-cache mode, undici no longer stores or re-serves responses containing Set-Cookie, including previously cached entries and revalidation paths.

Workarounds

Use a private cache (type: 'private') for per-user responses, or avoid caching responses that set cookies. Applications acting as shared caches should strip Set-Cookie from responses before caching.

References

@mcollina mcollina published to nodejs/undici Sep 4, 2026
Published by the National Vulnerability Database Sep 4, 2026
Published to the GitHub Advisory Database Sep 29, 2026
Reviewed Sep 29, 2026
Last updated Sep 29, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(21st percentile)

Weaknesses

Exposure of Sensitive Information to an Unauthorized Actor

The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. Learn more on MITRE.

Use of Cache Containing Sensitive Information

The code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere. Learn more on MITRE.

CVE ID

CVE-2026-84933

GHSA ID

GHSA-2jfj-6hjv-fm6j

Source code

Credits

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