# CVE-2026-66357: inets,httpd:HTTP Request Smuggling via obs-fold Header Continuation

Status: published. Published: 2026-09-01. Updated: 2026-11-11.

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, OTP 28.5.0.6, and OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, 9.6.2.3, and 9.7.2. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/erlang/otp/commit/220d618d2479a7180b4a06d0c5aacfaa4af4a85b
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/erlang/otp/commit/273d8958de38ff2a7fe0c5dcc5b6bfe6f65717f3
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/erlang/otp/commit/e640d599287d2eba919e6f13b91f042d7dbe6ff4

## Affected products and versions

- Erlang / OTP (otp): ≥ 17.0; < * (affected, otp); unaffected at 27.3.4.17; unaffected at 28.5.0.6; unaffected at 29.0.6. Source: CNA: EEF
- Erlang / OTP (inets): ≥ 5.10; < * (affected, otp); unaffected at 9.3.2.7; unaffected at 9.6.2.3; unaffected at 9.7.2. Source: CNA: EEF
- Erlang / OTP (erlang/otp): ≥ 84adefa331c4159d432d22840663c38f155cd4c1; < * (affected, git); unaffected at 220d618d2479a7180b4a06d0c5aacfaa4af4a85b; unaffected at 273d8958de38ff2a7fe0c5dcc5b6bfe6f65717f3; unaffected at e640d599287d2eba919e6f13b91f042d7dbe6ff4; ≥ 220d618d2479a7180b4a06d0c5aacfaa4af4a85b; < * (unaffected, git); ≥ 273d8958de38ff2a7fe0c5dcc5b6bfe6f65717f3; < * (unaffected, git); ≥ e640d599287d2eba919e6f13b91f042d7dbe6ff4; < * (unaffected, git). Source: CNA: EEF

## Severity and prioritization

- CVSS 4.0: 8.3 (high); 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; source: CNA: EEF

- CISA KEV: No listing in collected sources

- EPSS: 0.58% as of 2026-11-10; percentile 47.87%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-444

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/erlang/otp/security/advisories/GHSA-qh2f-33hj-37qf (CNA: EEF; vendor-advisory)

- https://cna.erlef.org/cves/CVE-2026-66357.html (CNA: EEF; related)

- https://osv.dev/vulnerability/EEF-CVE-2026-66357 (CNA: EEF; related)

- https://www.erlang.org/doc/system/versions.html#order-of-versions (CNA: EEF; x_version-scheme)

- https://github.com/erlang/otp/commit/220d618d2479a7180b4a06d0c5aacfaa4af4a85b (CNA: EEF; patch)

- https://github.com/erlang/otp/commit/273d8958de38ff2a7fe0c5dcc5b6bfe6f65717f3 (CNA: EEF; patch)

- https://github.com/erlang/otp/commit/e640d599287d2eba919e6f13b91f042d7dbe6ff4 (CNA: EEF; patch)

## Provenance

- CNA: EEF: https://www.cve.org/CVERecord?id=CVE-2026-66357; retrieved 2026-11-11; source updated 2026-11-11

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-66357; retrieved 2026-11-11; source updated Not reported

Revision: 6977f5552bddbfd82054865b7452fa2fd7d1ca1f945a18006f6b803e2e7702ef

Canonical: https://y2.dev/cve/CVE-2026-66357

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