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EEF-CVE-2026-23943
No affected components available
Summary
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 * zlib@openssh.com: 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 28.4.1, OTP 27.3.4.9 and OTP 26.2.5.18, corresponding to ssh from 3.0.1 before 5.5.1, 5.2.11.6 and 5.1.4.14.
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 zlib@openssh.com): {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)
Configuration
The SSH server or client must advertise zlib or zlib@openssh.com compression. Both are enabled by default. With zlib, the attack is pre-authentication; with zlib@openssh.com, authentication is required first.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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