CVE-2026-11525
ADVISORY - githubSummary
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=NoneOfYourBusinessis parsed asNone, the most permissive setting.SameSite=StrictLaxis parsed asLax, a downgrade fromStrict.
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.
Common Weakness Enumeration (CWE)
Permissive List of Allowed Inputs
Improper Validation of Syntactic Correctness of Input
GitHub
2.2
CVSS SCORE
3.7low| Package | Type | OS Name | OS Version | Affected Ranges | Fix Versions |
|---|---|---|---|---|---|
| undici | npm | - | - | >=7.0.0,<7.28.0 | 7.28.0 |
| undici | npm | - | - | <6.27.0 | 6.27.0 |
| undici | npm | - | - | >=8.0.0,<8.5.0 | 8.5.0 |
CVSS:3 Severity and metrics
The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.
The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).
A successful attack depends on conditions beyond the attacker's control, requiring investing a measurable amount of effort in research, preparation, or execution against the vulnerable component before a successful attack.
The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
The vulnerable system can be exploited without interaction from any user.
An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
There is no loss of confidentiality.
Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
There is no impact to availability within the impacted component.
Debian
-
Ubuntu
-
CVSS SCORE
N/AmediumRed Hat
2.2
CVSS SCORE
3.7lowChainguard
CGA-2rp4-x4w5-v2x2
-
minimos
MINI-5fjh-pxxq-qc5j
-
minimos
MINI-7m2m-g42c-2h44
-
minimos
MINI-93c5-v357-m8j4
-