EEF-CVE-2026-7790

Summary

Uncontrolled Resource Consumption vulnerability in ninenines cowlib (cowhttpte module) allows Excessive Allocation.

The chunked transfer-encoding parser in cowhttpte 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/cowhttpte.erl and program routines cowhttpte:streamchunked/2, cowhttpte:chunkedlen/4.

This issue affects cowlib: from 0.6.0 before 2.16.1.

Workaround

In Cowboy, setting initialstreamflow_size to a much lower value limits the amount of chunked body data that cowlib will parse in a single read, reducing the window of data an attacker can use to trigger the quadratic work. This does not fully eliminate the vulnerability but can significantly reduce its impact for some applications.