How severe is CVE-2026-11525?

CVE-2026-11525 has a CVSS score of 3.7/10, rated LOW. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-11525?

CVE-2026-11525 affects the following packages: undici (npm), undici (npm), undici (npm). Ecosystems affected: npm.

How do I fix CVE-2026-11525?

Update undici to 6.27.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-11525 is resolved across your whole dependency graph.

How do I detect CVE-2026-11525 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for undici, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-11525 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-11525 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-11525 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-11525?

CVE-2026-11525 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 14th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-11525?

CVE-2026-11525 is classified as CWE-183 (CWE-183). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-11525 published, and has it been updated?

CVE-2026-11525 was published on June 17, 2026 and was last updated on September 29, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

LOW severity

CVE-2026-11525 — undici

LOW

CVE-2026-11525 is a low-severity (CVSS 3.7) CWE-183 vulnerability in undici. A fix is available for undici — see the affected versions and patch details below.

undici vulnerable to Set-Cookie SameSite attribute downgrade via permissive substring matching

Also known asGHSA-g8m3-5g58-fq7m

Published

Jun 17, 2026

Updated

Sep 29, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Oct 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-11525.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs14th percentile — riskier than 14% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-11525 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 383,485 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

3 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

8Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

undicinpm

247.7Mdownloads / week

Description

Impact

When undici parses a Set-Cookie header, it accepts any SameSite attribute value that contains Strict, Lax, or None as a substring, rather than the case-insensitive exact match specified by RFC 6265. Non-spec values are silently mapped to one of the three standard tokens:

SameSite=NoneOfYourBusiness is parsed as None, the most permissive setting.
SameSite=StrictLax is parsed as Lax, a downgrade from Strict.

Affected applications are those that consume Set-Cookie headers from server responses (for example via undici's fetch or proxy code paths) and then forward or rely on the parsed sameSite attribute. A malicious or non-compliant server can coerce the consumer's view of a cookie's SameSite policy to a weaker value, silently degrading the SameSite enforcement the cookie is supposed to provide.

This was introduced in undici 5.15.0 when the cookies feature was added.

Patches

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

Workarounds

After parsing a Set-Cookie header, validate that the resulting sameSite attribute is one of 'Strict', 'Lax', or 'None' (exact, case-insensitive) before forwarding or relying on it.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`undici`	all versions	6.27.0`npm install undici@6.27.0`
📦npm	`undici`	≥ 7.0.0&&< 7.28.0	7.28.0`npm install undici@7.28.0`
📦npm	`undici`	≥ 8.0.0&&< 8.5.0	8.5.0`npm install undici@8.5.0`

Affected Products

1 product · 3 configurations

Application

undicinodejs

≥ 8.0.0 && < 8.5.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for undici, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update undici to 6.27.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-11525 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatLow

This Low impact flaw in undici, as used in various Red Hat products, arises from incorrect parsing of the `SameSite` cookie attribute. A malicious server could exploit this by sending a specially crafted `Set-Cookie` header, causing the `SameSite` policy to be downgraded to a less secure setting. This could lead to a…

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-11525 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat Enterprise Linux 10	`nodejs24-1:24.18.0-1.el10_2`	RHSA-2026:35841
Red Hat Enterprise Linux 10	`nodejs22-1:22.23.1-2.el10_2`	RHSA-2026:35842
Red Hat Enterprise Linux 8	`nodejs:24-8100020260630152626.6d880403`	RHSA-2026:39868
Red Hat Enterprise Linux 8	`nodejs:22-8100020260703140402.6d880403`	RHSA-2026:41947
Red Hat Enterprise Linux 9	`nodejs:24-9080020260626074955.rhel9`	RHSA-2026:35891
Red Hat Enterprise Linux 9	`nodejs:22-9080020260626075442.rhel9`	RHSA-2026:35892
Red Hat Hardened Images	`nodejs24-main-11.16.0-1.24.18.0.0.3.hum1`	RHSA-2026:38236
Red Hat Hardened Images	`nodejs26-main-11.17.0-1.26.5.0.1.5.hum1`	RHSA-2026:45783

Frequently Asked Questions

## Impact When undici parses a `Set-Cookie` header, it accepts any `SameSite` attribute value that contains `Strict`, `Lax`, or `None` as a substring, rather than the case-insensitive exact match specified by RFC 6265. Non-spec values are silently mapped to one of the three standard tokens: - `SameSite=NoneOfYourBusiness` is parsed as `None`, the most permissive setting. - `SameSite=StrictLax` is parsed as `Lax`, a downgrade from `Strict`. Affected applications are those that consume `Set-Cookie` headers from server responses (for example via undici's `fetch` or proxy code paths) and then f