cowlib vulnerabilities

CVE-2026-43970 is a vulnerability related to improper handling of highly compressed data in the cowlib library, which can lead to remote denial of service attacks via memory exhaustion. It allows unauthenticated users to send specially crafted SPDY frames that can cause significant memory consumption.

cowlib (Erlang) versions 2.9.0 through 2.20.0 fail to escape values inserted into the Link: header in cow_link:link/1. Special characters in the URI, rel, or attribute keys can be injected into the header, allowing additional Link directives to be smuggled. As a result, victim browsers may be forced to make connections to attacker-controlled resources.

A vulnerability in the cowlib library allows an unauthenticated remote attacker to exhaust memory on a vulnerable server or client by sending specially crafted HTTP/2 or HTTP/3 frames. The issue stems from missing limits in the HPACK and QPACK decoder, which processes arbitrarily long prefixed integers, causing large bignum allocations and heavy garbage collection churn.

A CRLF injection vulnerability in cowlib version 2.9.0 allows HTTP response splitting due to improper neutralization of non-VCHAR bytes in structured HTTP header values. The escape_string/2 function fails to escape CR and LF characters, enabling attackers to inject new headers into HTTP responses.

The cowlib Erlang library's cow_cookie:cookie/1 function builds a Cookie header without validating cookie names or values. This allows injection of ;, comma, CR, LF, or TAB characters, enabling cookie smuggling and HTTP request splitting. Affects versions from 2.9.0 before 2.21.0.