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Fencer Vulns
high 8.2

CVE-2026-55951 json

httpc memory exhaustion via unbounded response header accumulation

published 2026-09-01 2 mo ago modified 2026-09-08 2 mo ago also EUVD-2026-69228

cvss
8.2
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 53%
public exploits
0
none known

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 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.

Patch / fix

  • Erlang OTP 9.3.2.7, 9.6.2.3, 9.7.2, 27.3.4.17, 28.5.0.6, 29.0.6
  • erlang Debian 13 1:27.3.4.1+dfsg-1+deb13u4
  • erlang Debian 14 1:29.0.6+dfsg-1

debian advisories DEBIAN-CVE-2026-55951

  • erlang Ubuntu 22.04 LTS 1:24.2.1+dfsg-1ubuntu0.7
  • erlang Ubuntu 24.04 LTS 1:25.3.2.8+dfsg-1ubuntu4.7
  • erlang Ubuntu 26.04 LTS 1:27.3.4.6+dfsg-1ubuntu0.1
  • erlang Ubuntu Pro 14.04 LTS 1:16.b.3-dfsg-1ubuntu2.2+esm2
  • erlang Ubuntu Pro 16.04 LTS 1:18.3-dfsg-1ubuntu3.1+esm3
  • erlang Ubuntu Pro 18.04 LTS 1:20.2.2+dfsg-1ubuntu2+esm3
  • erlang Ubuntu Pro 20.04 LTS 1:22.2.7+dfsg-1ubuntu0.5+esm2

ubuntu advisories UBUNTU-CVE-2026-55951

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • erlang Azure Linux 3.0 26.2.5.21-6

azure linux advisories AZL-98454

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.69% chance of exploitation in the next 30 days, higher than 53% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 8.2 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
CNA 4.0 8.2 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

  • Erlang OTP

Classification

Weakness
  • CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.