CVE-2026-43970 Decompression Bomb in cow_spdy:inflate/2 Allows Memory Exhaustion via Crafted SPDY Frame
Unauthenticated attackers can cause memory exhaustion and denial of service in cowlib by sending crafted SPDY frames that decompress to excessive sizes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-43970?
CVE-2026-43970 is a high-severity denial of service vulnerability in ninenines cowlib, published on 13 May 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 (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.
Weakness: CWE-409
Which versions are affected by CVE-2026-43970?
3 open source packages ship an affected version, including cowlib.
| Package | Affected | Fixed in |
|---|---|---|
cowlib Hex | From 0.1.0 | 2.16.1 |
cowlib Hex | From 0.1.0 | 2.16.1 |
cowlib Hex | From 0.1.0 | 2.16.1 |
How do I fix CVE-2026-43970?
Upgrade cowlib to 2.16.1 or later.
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-2026-43970 being exploited?
There is no known exploitation of CVE-2026-43970 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-43970, EEF-CVE-2026-43970, GHSA-84f2-rp86-235p, UBUNTU-CVE-2026-43970.