---
id: CVE-2026-66357
title: >-
  httpd has never implemented obs-fold (RFC 2616 §2.2 / RFC 7230 §3.2.4 header
  continuation lines)
summary: >-
  httpd has never implemented obs-fold (RFC 2616 §2.2 / RFC 7230 §3.2.4 header
  continuation lines). Every CRLF followed by a non-CRLF octet unconditionally
  starts a new header. This missing feature became a security concern as the
  understa…
severity: high
cvss: 8.3
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:H/VA:N/SC:N/SI:L/SA:N'
cwe:
  - CWE-444
vendor: Erlang
product: otp
affected:
  - otp >= 17.0 < 27.3.4.17
  - otp >= 28.0 < 28.5.0.6
  - otp >= 29.0 < 29.0.6
  - inets >= 5.10 < 9.3.2.7
  - inets >= 9.4 < 9.6.2.3
  - inets >= 9.7 < 9.7.2
  - erlang/otp >= 84adefa331c4159d432d22840663c38f155cd4c1 < *
published: '2026-09-01'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T01:17:51.840'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-66357'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-66357.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/erlang/otp/commit/220d618d2479a7180b4a06d0c5aacfaa4af4a85b
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/erlang/otp/commit/273d8958de38ff2a7fe0c5dcc5b6bfe6f65717f3
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/erlang/otp/commit/e640d599287d2eba919e6f13b91f042d7dbe6ff4
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://github.com/erlang/otp/security/advisories/GHSA-qh2f-33hj-37qf'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-66357'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-01T15:56:00.806246Z'
cvssSource: cna
epss: 0.00577
epssPercentile: 0.45199
ingestedAt: '2026-09-08T15:33:26.956Z'
---

## Overview

httpd has never implemented obs-fold (RFC 2616 §2.2 / RFC 7230 §3.2.4 header continuation lines). Every CRLF followed by a non-CRLF octet unconditionally starts a new header. This missing feature became a security concern as the understanding of HTTP request smuggling attacks evolved.

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.