httpc memory exhaustion via unbounded response header accumulation
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- Present
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Fixed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-770.
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Erlang | OTP | 17.0 to before 27.3.4.17; 28.0 to before 28.5.0.6; 29.0 to before 29.0.6 | 27.3.4.17, 28.5.0.6, 29.0.6 | Patch available | CNA |
| Erlang | OTP | 5.10 to before 9.3.2.7; 9.4 to before 9.6.2.3; 9.7 to before 9.7.2 | 9.3.2.7, 9.6.2.3, 9.7.2 | Patch available | CNA |
- OTP VendorErlang Affected 17.0 to before 27.3.4.17; 28.0 to before 28.5.0.6; 29.0 to before 29.0.6 Fixed in 27.3.4.17, 28.5.0.6, 29.0.6 Patch available CNA
- OTP VendorErlang Affected 5.10 to before 9.3.2.7; 9.4 to before 9.6.2.3; 9.7 to before 9.7.2 Fixed in 9.3.2.7, 9.6.2.3, 9.7.2 Patch available CNA
Remediation
- Fix · CNA OTP (Erlang) Fixed in 27.3.4.17, 28.5.0.6, 29.0.6
- Fix · CNA OTP (Erlang) Fixed in 9.3.2.7, 9.6.2.3, 9.7.2
Fixed in the same release
Records fixed by the same vendor advisory or release, as the CNA lists them.
- Release ·
Erlang OTP 17.0, 27.3.4.17 and 2 more versions
11 records Highest priority Priority MEDIUM 2 MEDIUM, 9 LOW
Other records, highest priority first
- TI-2026-50021 httpd applies no timeout while receiving a request body, parking a worker on a stalled clientPriority MEDIUM 45
- TI-2026-52570 inets,httpd: Memory Exhaustion via Unenforced max_body_size During Chunked Body ReceptionPriority MEDIUM 44
- TI-2026-47459 httpd mod_auth directory protection bypassed by a doubled slash in the request pathPriority LOW 38
- Release ·
Erlang OTP 5.10, 9.3.2.7 and 2 more versions
9 records Highest priority Priority MEDIUM 2 MEDIUM, 7 LOW
Other records, highest priority first
- TI-2026-50021 httpd applies no timeout while receiving a request body, parking a worker on a stalled clientPriority MEDIUM 45
- TI-2026-52570 inets,httpd: Memory Exhaustion via Unenforced max_body_size During Chunked Body ReceptionPriority MEDIUM 44
- TI-2026-47459 httpd mod_auth directory protection bypassed by a doubled slash in the request pathPriority LOW 38
Timeline
- 2026-10-02 Threatist record created from CVE-2026-55951
References
Patch 2
More Erlang vulnerabilities
- TI-2025-23504 Erlang/OTP SSH Vulnerable to Pre-Authentication RCE KEVCVSS 3.1CRITICAL 10.0
- TI-2026-48954 httpd parks a request worker indefinitely on a malformed chunk size sent after the headers CVSS 4.0HIGH 8.7
- TI-2023-26623 The SSH transport protocol with certain OpenSSH extensions, found in OpenSSH before 9.6… CVSS 3.1MEDIUM 5.9
- TI-2026-71037 Path traversal in rebar3 via unvalidated dependency app names CVSS 4.0HIGH 7.5
- TI-2024-36042 ssl fails to validate incorrect extened key usage CVSS 3.1MEDIUM 5.5
- TI-2020-10791 Rebar3 versions 3.0.0-beta.3 to 3.13.2 are vulnerable to OS command injection via URL… CVSS 3.1CRITICAL 9.8
Sources
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences