CVE-2026-23943
Pre-auth SSH DoS via unbounded zlib inflate
Improper Handling of Highly Compressed Data (Compression Bomb) vulnerability in Erlang OTP ssh (ssh_transport modules) allows Denial of Service via Resource Depletion. The SSH transport layer advertises legacy zlib compression by default and inflates attacker-controlled payloads pre-authentication without any size limit, enabling reliable memory exhaustion DoS. Two compression algorithms are affected: * zlib: Activates immediately after key exchange, enabling unauthenticated attacks * [email protected]: Activates post-authentication, enabling authenticated attacks Each SSH packet can decompress ~255 MB from 256 KB of wire data (1029:1 amplification ratio). Multiple packets can rapidly exhaust available memory, causing OOM kills in memory-constrained environments. This vulnerability is associated with program files lib/ssh/src/ssh_transport.erl and program routines ssh_transport:decompress/2, ssh_transport:handle_packet_part/4. This issue affects OTP from OTP 17.0 before OTP 26.2.5.18, OTP 27.3.4.9, and OTP 28.4.1, corresponding to ssh from 3.0.1 before 5.1.4.14, 5.2.11.6, and 5.5.1.
Fixes and workarounds
Workaround
Best workaround - Disable all compression: {preferred_algorithms, [{compression, ['none']}]} Alternative mitigations (less secure): * Disable only pre-auth zlib compression (authenticated users can still exploit via [email protected]): {modify_algorithms, [{rm, [{compression, ['zlib']}]}]} * Limit concurrent sessions (reduces attack surface but does not prevent exploitation): {max_sessions, N} % Cap total concurrent sessions (default is infinity)
Source: CNA: EEFFix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: EEFFix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: EEFFix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: EEFAffected products and versions
| Product | Versions | Authority |
|---|---|---|
| OTP Erlang otp
software-id |
≥ 17.0; < * (affected, otp); unaffected at 26.2.5.18; unaffected at 27.3.4.9; unaffected at 28.4.1
Other versions: unaffected |
CNA: EEF |
| OTP Erlang ssh
otp |
≥ 3.0.1; < * (affected, otp); unaffected at 5.1.4.14; unaffected at 5.2.11.6; unaffected at 5.5.1
Other versions: unaffected |
CNA: EEF |
| OTP Erlang erlang/otp
github |
≥ 07b8f441ca711f9812fad9e9115bab3c3aa92f79; < * (affected, git); unaffected at 0c1c04b191f6ab940e8fcfabce39eb5a8a6440a4; unaffected at 93073c3bd338c60cd2bae715ce6a1d4ffc1a8fd3; unaffected at 43a87b949bdff12d629a8c34146711d9da93b1b1
Other versions: unaffected |
CNA: EEF |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 4.0 / 6.9 medium |
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N | CNA: EEF |
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://github.com/erlang/otp/security/advisories/GHSA-c836-qprm-jw9rCNA: EEF · vendor-advisory, related
- https://cna.erlef.org/cves/CVE-2026-23943.htmlCNA: EEF · related
- https://osv.dev/vulnerability/EEF-CVE-2026-23943CNA: EEF · related
- https://www.erlang.org/doc/system/versions.html#order-of-versionsCNA: EEF · x_version-scheme
- https://github.com/erlang/otp/commit/07b8f441ca711f9812fad9e9115bab3c3aa92f79CNA: EEF · related
- https://github.com/erlang/otp/commit/0c1c04b191f6ab940e8fcfabce39eb5a8a6440a4CNA: EEF · patch
- https://github.com/erlang/otp/commit/93073c3bd338c60cd2bae715ce6a1d4ffc1a8fd3CNA: EEF · patch
- https://github.com/erlang/otp/commit/43a87b949bdff12d629a8c34146711d9da93b1b1CNA: EEF · patch
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