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CVE-2026-84933

MEDIUMCVSS 6.5/10EPSS 0.25%

Last modified

CVE-2026-84933 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. undici's cache interceptor does not handle the Set-Cookie response header anywhere in its cache path, so it neither refuses to store nor strips that header. In shared cache mode, which is the default, an otherwise cacheable response that carries a Set-Cookie header, for example one marked with a public and max-age directive, is stored and then re-served to a later caller that matches the same cache key. EPSS estimates a 0.25% chance of exploitation in the next 30 days.

Description

undici's cache interceptor does not handle the Set-Cookie response header anywhere in its cache path, so it neither refuses to store nor strips that header. In shared cache mode, which is the default, an otherwise cacheable response that carries a Set-Cookie header, for example one marked with a public and max-age directive, is stored and then re-served to a later caller that matches the same cache key. As a result one caller's cookie is disclosed to a different caller, and an untrusted server can inject cookies into cached responses served to all subsequent callers. This violates the requirement that a shared cache must not store cookies. This affects undici versions from 7.0.0 up to 7.29.1 and from 8.0.0 up to 8.10.2. Users should upgrade to undici 7.29.1 or 8.10.2.

Metrics

CVSS 3.1
6.5/10

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

EPSS Probability
0.25%

15.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
undiciundici>= 7.0.0, < 7.29.1; >= 8.0.0, < 8.10.2

References

Timeline

Published
Last Modified
Status
Awaiting Analysis

Frequently Asked Questions

What is CVE-2026-84933?
undici's cache interceptor does not handle the Set-Cookie response header anywhere in its cache path, so it neither refuses to store nor strips that header. In shared cache mode, which is the default, an otherwise cacheable response that carries a Set-Cookie header, for example one marked with a public and max-age directive, is stored and then re-served to a later caller that matches the same cache key. As a result one caller's cookie is disclosed to a different caller, and an untrusted server can inject cookies into cached responses served to all subsequent callers. This violates the requirement that a shared cache must not store cookies. This affects undici versions from 7.0.0 up to 7.29.1 and from 8.0.0 up to 8.10.2. Users should upgrade to undici 7.29.1 or 8.10.2.
How severe is CVE-2026-84933?
CVE-2026-84933 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.25% probability of exploitation in the next 30 days.
How do I fix CVE-2026-84933?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST