cowlib vulnerabilities

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 vulnerability in the cowlib library (from version 2.9.0 onward) involves improper neutralization of CRLF sequences in HTTP headers, enabling HTTP response splitting attacks. The cow_http_struct_hd:escape_string/2 function in cowlib only escapes \ and ", passing all other bytes through verbatim, creating an encoder/decoder asymmetry. An attacker can inject \r\n into the serialized header, allowing new headers to be added and potentially splitting the HTTP response.

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.

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.

cowlib versions 2.6.0 to before 2.16.1 contain a CRLF injection vulnerability allowing SSE event splitting and injection via unvalidated field values. An attacker can inject additional SSE lines and forge a complete event with arbitrary type and data.