Executive brief
Erlang's OTP inets library, which provides HTTP server functionality for applications built on Erlang, contains a flaw in HTTP request parsing that allows attackers to bypass input validation through malformed headers. This vulnerability enables HTTP request smuggling attacks, where an attacker can inject crafted requests that are interpreted differently by proxies and backend servers, potentially leading to cache poisoning, session hijacking, or unauthorized access to protected resources.
Technical details
This vulnerability (CWE-444) stems from a flaw in the "gracefulness" code of the inets HTTP parser that fails to reject certain malformed HTTP headers, specifically those with whitespace before the colon delimiter. Instead of properly validating and rejecting these cases, the parser silently drops or mishandles them, leading to inconsistent interpretation between different HTTP implementations. An attacker can craft requests with whitespace-before-colon headers that are accepted by the Erlang inets server but interpreted differently by upstream proxies or other HTTP agents, enabling request smuggling attacks. The vulnerability is network-accessible with no authentication required; exploitation does require precise timing and knowledge of the downstream stack (AT:P). Patches are available in OTP 27.3.4.17+, 28.5.0.6+, and 29.0.6+, corresponding to inets 9.3.2.7+, 9.6.2.3+, and 9.7.2+.
Affected products
- Erlang OTP 22.2 before 27.3.4.17, 28.0 before 28.5.0.6, 29.0 before 29.0.6
- Erlang inets 7.1.2 before 9.3.2.7, 9.4 before 9.6.2.3, 9.7 before 9.7.2
Timeline
- 2026-09-01: disclosed
- 2026-09-01: patched: Patches available as OTP 27.3.4.17, 28.5.0.6, 29.0.6