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Vulnerability · Published Mar 13, 2026 · Assigned by EEF

CVE-2026-23943Pre-auth SSH DoS via unbounded zlib inflate

Medium 6.9

In plain English

A medium-severity security flaw in OTP from Erlang. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 53% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)6.9Medium
Exploit odds (30 days)0.7%top 47.3% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

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 * 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12erlang1:25.2.3+dfsg-1+deb12u4DEBIAN-CVE-2026-23943
Debian:13erlang1:27.3.4.1+dfsg-1+deb13u2DEBIAN-CVE-2026-23943
Debian:14erlang1:27.3.4.9+dfsg-1DEBIAN-CVE-2026-23943
Ubuntu:22.04:LTSerlang1:24.2.1+dfsg-1ubuntu0.8USN-8901-1
Ubuntu:22.04:LTSerlang1:24.2.1+dfsg-1ubuntu0.8UBUNTU-CVE-2026-23943
Ubuntu:24.04:LTSerlang1:25.3.2.8+dfsg-1ubuntu4.8USN-8901-1
Ubuntu:24.04:LTSerlang1:25.3.2.8+dfsg-1ubuntu4.8UBUNTU-CVE-2026-23943
Ubuntu:25.10erlangno fix listedUBUNTU-CVE-2026-23943
Ubuntu:26.04:LTSerlang1:27.3.4.6+dfsg-1ubuntu0.2UBUNTU-CVE-2026-23943
Ubuntu:26.04:LTSerlang1:27.3.4.6+dfsg-1ubuntu0.2USN-8901-1

Affected products (as reported)

VendorProductVersions
Erlang OTP 3.0.1 – before *
Erlang OTP 17.0 – before *07b8f441ca711f9812fad9e9115bab3c3aa92f79 – before *

Weakness: CWE-409 · Vector: 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

References