CVE-2026-15157: undici vulnerable to CRLF Injection via blob-like body 'type' property

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-29 · updated 2026-08-04
Weakness: CWE-93

Description

undici does not validate the type property of a duck-typed blob-like request body before using it as the Content-Type header on the HTTP/1.1 dispatcher. In undici before 6.28.0, from 7.0.0 up to before 7.29.0, and from 8.0.0 up to before 8.9.0, an application that passes a hand-rolled blob-like body (via request, stream, pipeline, or dispatch) whose type is derived from untrusted input allows an attacker to inject CRLF sequences and append arbitrary HTTP headers, potentially smuggling a second request past the upstream. Native Blob objects are safe because their constructor strips CRLF from the type, and fetch is unaffected because it validates headers, but ecosystem libraries that build duck-typed blob shapes from user input can reach the vulnerable path. This is the same defect class as CVE-2022-35948 and CVE-2026-1527, on a header sink that the earlier fixes did not cover. The issue is fixed in undici 6.28.0, 7.29.0, and 8.9.0.

Affected products

undici: before 6.28.0; from 7.0.0 before 7.29.0; from 8.0.0 before 8.9.0 — fixed in 6.28.0, 7.29.0, 8.9.0
Npm Undici: before 6.28.0; from 7.0.0 before 7.29.0; from 8.0.0 before 8.9.0 — fixed in 6.28.0, 7.29.0, 8.9.0

How to fix

Upgrade to a fixed version: undici 6.28.0, 7.29.0, 8.9.0; Npm Undici 6.28.0, 7.29.0, 8.9.0. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-15157 or the next vulnerability affects your stack