Vulnerability · Published May 11, 2026 · Assigned by EEF
CVE-2026-7790Unbounded chunk-size hex digits in cowlib cause quadratic CPU and memory DoS
High 8.7
In plain English
A high-severity uncontrolled resource consumption in cowlib from ninenines. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 37% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | erlang-cowlib | no fix listed | DEBIAN-CVE-2026-7790 |
| Debian:13 | erlang-cowlib | no fix listed | DEBIAN-CVE-2026-7790 |
| Debian:14 | erlang-cowlib | 2.17.1-1 | DEBIAN-CVE-2026-7790 |
| Ubuntu:22.04:LTS | erlang-cowlib | no fix listed | UBUNTU-CVE-2026-7790 |
| Ubuntu:24.04:LTS | erlang-cowlib | no fix listed | UBUNTU-CVE-2026-7790 |
| Ubuntu:25.10 | erlang-cowlib | no fix listed | UBUNTU-CVE-2026-7790 |
| Ubuntu:26.04:LTS | erlang-cowlib | no fix listed | UBUNTU-CVE-2026-7790 |
| Ubuntu:26.10 | erlang-cowlib | no fix listed | UBUNTU-CVE-2026-7790 |
Affected products (as reported)
Weakness: CWE-400 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
References
- https://cna.erlef.org/cves/CVE-2026-7790.html related, third-party-advisory
- https://osv.dev/vulnerability/EEF-CVE-2026-7790 related
- https://github.com/ninenines/cowlib/commit/a4b8039ce8c93ab00867ef6b7e888822c09f4369 patch