# CVE-2026-43970: ninenines cowlib denial of service via SPDY decompression bomb

Source: https://junglewise.ai/threats/cve-2026-43970-ninenines-cowlib-denial-of-service-via-spdy-decompression-bomb  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-05-19  
License: CC BY 4.0 with a link back

CVE-2026-43970 · Severity: high · CVSS 8.2 · Published 2026-05-13

A vulnerability in the cowlib Erlang library allows an attacker to crash a server by sending a specially crafted SPDY data frame. This library is used for manipulating web protocols, and the flaw can lead to a complete service outage by exhausting the server's memory. Organizations using this library in applications that process SPDY traffic are at risk of a remote denial-of-service attack.

Technologies: [Nine Nines Cowlib](https://junglewise.ai/threats/technologies/cowlib). Vendors: [Nine Nines](https://junglewise.ai/threats/vendors/nine-nines).

## Quick answers

**Is CVE-2026-43970 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-43970 being exploited in the wild.

**How severe is CVE-2026-43970?** High severity, with a CVSS score of 8.2, published 13 May 2026.

**Which products and versions are affected?** Nine Nines Cowlib >= 0.1.0, < 2.16.1, 0.1.0 before 2.16.1.

**Is there a fix for CVE-2026-43970?** A patch was published on 2026-05-19: GitHub advisory reviewed and updated with patch details Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-43970 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-43970?** Check whether you run Nine Nines Cowlib at an affected version. 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 cow_spdy:inflate/2 function in cowlib fails to implement output size bounds when passing peer-supplied compressed bytes to zlib:inflate/2. Because the SPDY header compression dictionary is public, an attacker can craft a small SPDY frame (a few kilobytes) that expands to several gigabytes on the BEAM heap, leading to an Out-Of-Memory (OOM) termination of the node. The vulnerability affects the parsers for syn_stream, syn_reply, and headers frame types via cow_spdy:parse_headers/2. The issue was resolved in version 2.16.1 by completely removing the deprecated cow_spdy module.

## Affected products

- ninenines cowlib >= 0.1.0, < 2.16.1

## Identifiers

- CVE-2026-43970
- GHSA-84f2-rp86-235p

## Timeline

- 2026-05-13: advisory: Initial publication of GHSA-84f2-rp86-235p
- 2026-05-13: disclosed: CVE-2026-43970 published
- 2026-05-19: patched: GitHub advisory reviewed and updated with patch details

## References

- [https://github.com/ninenines/cowlib/commit/16aad3fb9f81f5cda4d1706ff0c54237c619c282](https://github.com/ninenines/cowlib/commit/16aad3fb9f81f5cda4d1706ff0c54237c619c282)
- [https://cna.erlef.org/cves/CVE-2026-43970.html](https://cna.erlef.org/cves/CVE-2026-43970.html)

## Related threats

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