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Erlang HTTP server can misinterpret duplicate length headers

published 2 months ago
Summary

Certain older versions of Erlang’s HTTP component may treat mismatched Content‑Length and Transfer‑Encoding headers incorrectly, which can let an attacker slip extra requests past the server. This can cause request smuggling, potentially exposing internal systems to unauthorized actions. Upgrade Erlang to the latest release or apply the vendor’s security update to resolve the issue.

What to do
  • Update azure erlang to version 26.2.5.21-6.
Affected software
Ecosystem VendorProductAffected versions
Azure Linux:3 azure erlang < 26.2.5.21-6
Fix: upgrade to 26.2.5.21-6
Original advisory text
CVE-2026-73812 affecting package erlang for versions less than 26.2.5.21-6
httpd function check_header/3 rejects duplicate Content-Length (per CVE-2026-23941) but never checks for the TE+CL co-presence that RFC 9112 §6.3 identifies as a probable smuggling attempt. handle_body/3 frames by chunked and silently discards Content-Length. A CL-preferring front-end paired with chunked-preferring inets creates a classic CL.TE front-end/back-end desync.

This issue affects OTP from OTP 17.0 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.
References
Timeline
Published1 Sep 2026
Updated23 Sep 2026
First seen23 Sep 2026
Sources
AZL-98490 · OSV
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