# CVE-2026-23943: Erlang OTP SSH denial of service via zlib compression bomb

Source: https://junglewise.ai/threats/cve-2026-23943-erlang-otp-ssh-denial-of-service-via-zlib-compression-bomb  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-13. Updated: 2026-05-21  
License: CC BY 4.0 with a link back

CVE-2026-23943 · Severity: medium · CVSS 5.3 · Published 2026-03-13

A vulnerability in the Erlang SSH library allows an attacker to crash or disable services by sending specially crafted, highly compressed data. This 'compression bomb' can exhaust a server's memory, leading to a denial of service that prevents legitimate users from accessing the system. Because the flaw can be triggered before a user even logs in, it poses a significant risk to any publicly accessible Erlang-based SSH service.

## Quick answers

**Is CVE-2026-23943 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-23943 being exploited in the wild.

**How severe is CVE-2026-23943?** Medium severity, with a CVSS score of 5.3, published 13 March 2026.

**Which products and versions are affected?** Erlang OTP 17.0 to 26.2.5.17, 27.0 to 27.3.4.8, 28.0 to 28.4.0; Erlang ssh 3.0.1 to 5.1.4.13, 5.2 to 5.2.11.5, 5.5 to 5.5.0.

**Is there a fix for CVE-2026-23943?** A patch was published on 2026-03-12: Fixes merged into maintenance branches. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-23943 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-23943?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The Erlang OTP SSH transport layer (ssh_transport modules) fails to impose size limits on decompressed data when using zlib compression. An attacker can send a 'compression bomb'—a small payload that expands significantly upon decompression (up to a 1029:1 ratio)—to trigger an Out-of-Memory (OOM) condition. The 'zlib' algorithm is enabled by default and operates pre-authentication, allowing unauthenticated remote attackers to exhaust memory. The 'zlib@openssh.com' algorithm is also affected but requires successful authentication. The issue is fixed in OTP versions 28.4.1, 27.3.4.9, and 26.2.5.18 by disabling zlib by default and implementing decompression size limits.

## Affected products

- Erlang OTP 17.0 to 26.2.5.17, 27.0 to 27.3.4.8, 28.0 to 28.4.0
- Erlang ssh 3.0.1 to 5.1.4.13, 5.2 to 5.2.11.5, 5.5 to 5.5.0

## Timeline

- 2026-03-12: patched: Fixes merged into maintenance branches.
- 2026-03-13: disclosed: Initial vulnerability disclosure.
- 2026-03-13: advisory: NVD and Vendor advisories published.

## References

- [https://cna.erlef.org/cves/CVE-2026-23943.html](https://cna.erlef.org/cves/CVE-2026-23943.html)
- [https://github.com/erlang/otp/commit/0c1c04b191f6ab940e8fcfabce39eb5a8a6440a4](https://github.com/erlang/otp/commit/0c1c04b191f6ab940e8fcfabce39eb5a8a6440a4)
- [https://github.com/erlang/otp/commit/43a87b949bdff12d629a8c34146711d9da93b1b1](https://github.com/erlang/otp/commit/43a87b949bdff12d629a8c34146711d9da93b1b1)
- [https://github.com/erlang/otp/commit/93073c3bd338c60cd2bae715ce6a1d4ffc1a8fd3](https://github.com/erlang/otp/commit/93073c3bd338c60cd2bae715ce6a1d4ffc1a8fd3)
- [https://github.com/erlang/otp/security/advisories/GHSA-c836-qprm-jw9r](https://github.com/erlang/otp/security/advisories/GHSA-c836-qprm-jw9r)
- [https://www.erlang.org/doc/system/versions.html](https://www.erlang.org/doc/system/versions.html)