CVE-2026-15157

CVE-2026-15157 is a medium-severity vulnerability in Nodejs Undici with a CVSS 3.x base score of 4.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-93.

Key facts

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.

Frequently asked questions

What is CVE-2026-15157?
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.
How severe is CVE-2026-15157?
CVE-2026-15157 has a CVSS 3.x base score of 4.2, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-15157 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (8th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-15157?
CVE-2026-15157 affects Nodejs Undici. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-15157?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2026-15157 published?
CVE-2026-15157 was published on 2026-07-29 and last updated on 2026-08-04.

References

Affected products (1)

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