---
id: CVE-2026-55951
title: >-
  The Erlang/OTP httpc HTTP client does not enforce a limit on the total size of
  response headers received from a server
summary: >-
  The Erlang/OTP httpc HTTP client does not enforce a limit on the total size of
  response headers received from a server. The max_header_size option defaults
  to nolimit, and httpc_response:parse_headers/6 accumulates every header into a
  li…
severity: high
cvss: 8.2
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'
cwe:
  - CWE-770
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: '2026-09-08T01:17:50.477'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-55951'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-55951.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/erlang/otp/commit/aba0fe8c2d700bf4ac94607cf7f00e53bbe4042d
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/erlang/otp/commit/e3be1cfe9f6cedd0cd20d9905e05601dfb31c8aa
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://github.com/erlang/otp/security/advisories/GHSA-f9fw-mg7q-4g3x'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-55951'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://www.erlang.org/doc/system/versions.html#order-of-versions'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-01T15:53:49.437447Z'
cvssSource: cna
epss: 0.00382
epssPercentile: 0.32109
ingestedAt: '2026-09-08T15:33:26.956Z'
---

## Overview

The Erlang/OTP httpc HTTP client does not enforce a limit on the total size of response headers received from a server. The max_header_size option defaults to nolimit, and httpc_response:parse_headers/6 accumulates every header into a list before the length check runs (which only fires after the terminating CRLF CRLF is received).

A malicious or compromised HTTP server can send an arbitrarily large number of headers, or headers with very large values, causing the client process to allocate unbounded memory until the system runs out of memory or the BEAM VM crashes. A proof-of-concept server sending 100,000 headers of roughly 4000 bytes each caused the client VM to allocate over 13 GB of memory in under 30 seconds.

Any application using httpc:request/4,5 to connect to untrusted servers is affected. No authentication is required: any server the client connects to (including via a redirect or man-in-the-middle) can trigger the exhaustion.

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.