CVE-2026-23943 Pre-auth SSH DoS via unbounded zlib inflate
Unbounded zlib inflation in Erlang OTP SSH allows pre-authentication attackers to cause memory exhaustion and denial of service via compression bombs.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23943?
CVE-2026-23943 is a medium-severity denial of service vulnerability in Erlang OTP, published on 13 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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 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.
Weakness: CWE-409
Which versions are affected by CVE-2026-23943?
It affects 2 products.
Products include Erlang Erlang\/Otp, Erlang Erlang\/Ssh.
How do I fix CVE-2026-23943?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-23943 being exploited?
There is no known exploitation of CVE-2026-23943 in the wild and no public exploit code.
Other vulnerabilities in Erlang OTP
- CVE-2022-37026 Auth bypass in n/a
- CVE-2016-10253 Memory corruption in n/a
- CVE-2026-55953 TLS 1.2 and DTLS client accepts unoffered anonymous cipher suite, bypassing server authentication
- CVE-2026-49759 Stack buffer overflow in SCTP error cause parsing in inet_drv allows remote VM crash
- CVE-2026-58227 TLS/DTLS denial of service via unbounded recursion on cross-signed peer certificate chain
Sources
Also known as AZL-79877, DEBIAN-CVE-2026-23943, EEF-CVE-2026-23943, GHSA-c836-qprm-jw9r, UBUNTU-CVE-2026-23943.