Vulnerability advisory

EEF-CVE-2026-43970

Decompression Bomb in cow_spdy:inflate/2 Allows Memory Exhaustion via Crafted SPDY Frame

Published May 13, 2026Updated Sep 8, 2026OSV record ↗

Also known as CVE-2026-43970GHSA-84f2-rp86-235p

Severity

CVSS 4.0CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Affected versions

cowlib Hex

All cowlib advisories →

Affected	Fixed in
`0.1.0` to before 2.16.1	`2.16.1`Advisories →
Also listed as affected (32) `1.0.0` `1.0.1` `1.0.2` `1.1.0` `1.2.0` `1.3.0` `2.0.0` `2.0.1` `2.1.0` `2.10.0` `2.10.1` `2.11.0` `2.12.0` `2.12.1` `2.13.0` `2.14.0` `2.15.0` `2.16.0` `2.2.0` `2.2.1` `2.3.0` `2.4.0` `2.5.0` `2.5.1` `2.6.0` `2.7.0` `2.7.1` `2.7.2` `2.7.3` `2.8.0` `2.9.0` `2.9.1`

Repository

Affected commits	Fixed by commit
GIT github.com/ninenines/cowlib ↗
fad5c0049df278cc498b6cdb519b09e845a070a8 to before 16aad3fb9f81f5cda4d1706ff0c54237c619c282	`16aad3fb9f81f5cda4d1706ff0c54237c619c282`
Also listed as affected (42) `2.16.0` `2.15.0` `2.14.0` `2.13.0` `2.12.1` `2.12.0` `2.11.0` `2.10.1` `2.10.0` `2.9.1` `2.9.0` `2.8.0` `2.7.3` `2.7.2` `2.7.1` `2.7.0` `2.6.0` `2.5.1` `2.5.0` `2.4.0` `2.3.0` `2.2.1` `2.2.0` `2.1.0` `2.0.1` `2.0.0` `2.0.0-rc.1` `2.0.0-pre.1` `1.0.1` `1.3.0` `1.2.0` `1.1.0` `1.0.0` `0.6.2` `0.6.1` `0.6.0` `0.5.1` `0.5.0` `0.4.0` `0.3.0` `0.2.0` `0.1.0`

Description

Summary

Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in ninenines cowlib allows unauthenticated remote denial of service via memory exhaustion.

cow_spdy:inflate/2 in cowlib passes peer-supplied compressed bytes directly to zlib:inflate/2 with no output size bound. The SPDY header compression dictionary (?ZDICT) is public, and zlib compresses long runs of repeated bytes at roughly 1024:1, so a few kilobytes of SPDY frame payload can decompress to gigabytes on the BEAM heap, OOM-killing the node. A single unauthenticated SPDY frame is sufficient to trigger the condition. The parsers for syn_stream, syn_reply, and headers frame types are all affected via cow_spdy:parse_headers/2.

This issue affects cowlib from 0.1.0 before 2.16.1.

Configurations

The application must use cow_spdy:parse/2 to parse SPDY frames from an untrusted peer. cowboy itself does not use cow_spdy; only direct callers of the cow_spdy API are affected.

Solutions

Upgrade to cowlib 2.16.1 or later, in which the cow_spdy module has been removed entirely. No patched version of cow_spdy will be provided. Migrate away from SPDY, which has been deprecated since 2015 in favour of HTTP/2.