# CVE-2026-7790: Unbounded chunk-size hex digits in cowlib cause quadratic CPU and memory DoS

CVE-2026-7790 is fixed in erlang-cowlib on 1 platform by DEBIAN-CVE-2026-7790 (version 2.17.1-1), released May 11, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-7790
- Priority: High
- CVSS: 7.5 (Moderate)
- EPSS: 0.0043
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 11, 2026
- Weakness: Uncontrolled Resource Consumption
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-7790

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | erlang-cowlib Debian 14 | 2.17.1-1 | [DEBIAN-CVE-2026-7790](https://patchblox.com/security/data/fix/linux/debian-cve-2026-7790.md) | May 11, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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