GHSA-46q4-43ph-c6fr: org.http4s:blaze-http_2.13 (CVE-2026-73495)

Package	Ecosystem	Affected	Fixed in
org.http4s:blaze-http_2.13	Maven	<0.23.18 \|\| >=1.0.0-M1, <1.0.0-M42	0.23.18, 1.0.0-M42
org.http4s:blaze-http_2.12	Maven	<0.23.18	0.23.18
org.http4s:blaze-http_3	Maven	<0.23.18 \|\| >=1.0.0-M1, <1.0.0-M42	0.23.18, 1.0.0-M42

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Blaze-http (Maven org.http4s:blaze-http_2.13, _2.12 and _3) is affected in versions before 0.23.18 and from 1.0.0-M1 up to 1.0.0-M42, where blaze-server can copy HTTP/1.1 chunked-body trailer fields into request headers. An unauthenticated remote client can use this to add arbitrary headers, such as X-Forwarded-For or internal-auth headers, that a fronting proxy had removed, which can bypass header-based trust decisions in the application. Upgrade to 0.23.18 or 1.0.0-M42. If upgrading is not possible, deploy behind a proxy that strips trailer fields or rejects requests that use them.

Written 2 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
7.4	High	3.1	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N	CNA (GitHub_M)

CISA KEV Not listed.
EPSS 0.0048, the 41st percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:19 UTC First seen by agentprime
31 Oct 2026, 14:19 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.