CVE-2026-7790 Unbounded chunk-size hex digits in cowlib cause quadratic CPU and memory DoS
Remote attackers can cause denial of service via CPU and memory exhaustion by sending crafted chunked HTTP requests to applications using the cowlib library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-7790?
CVE-2026-7790 is a high-severity denial of service vulnerability in ninenines cowlib, published on 11 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Uncontrolled Resource Consumption vulnerability in ninenines cowlib (cow_http_te module) allows Excessive Allocation.
The chunked transfer-encoding parser in cow_http_te accepts an unbounded number of hex digits in the chunk-size field. Each digit causes a bignum multiplication (Len * 16 + digit), so parsing N hex digits requires O(N²) CPU work and O(N) memory. Additionally, when input is drip-fed, the parser discards the accumulated length on each partial read and restarts from zero on resumption, raising the cost to O(N³). An unauthenticated remote attacker can exploit this by sending an HTTP/1.1 request with Transfer-Encoding: chunked and a very long chunk-size hex string to cause denial of service through CPU exhaustion and memory amplification.
This vulnerability is associated with program file src/cow_http_te.erl and program routines cow_http_te:stream_chunked/2, cow_http_te:chunked_len/4.
This issue affects cowlib: from 0.6.0 before 2.16.1.
Weakness: CWE-400
Which versions are affected by CVE-2026-7790?
3 open source packages ship an affected version, including cowlib. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
cowlib Hex | From 0.6.0 | 2.16.1 |
cowlib Hex | From 0.6.0 | 2.16.1 |
cowlib Hex | From 0.6.0 | 2.16.1 |
Products include Ninenines Cowlib.
How do I fix CVE-2026-7790?
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-2026-7790 being exploited?
There is no known exploitation of CVE-2026-7790 in the wild and no public exploit code.
Other vulnerabilities in ninenines cowlib
Sources
Also known as AZL-86790, DEBIAN-CVE-2026-7790, EEF-CVE-2026-7790, GHSA-32p9-57cr-4x65, UBUNTU-CVE-2026-7790.