ninenines cowlib HPACK Decoder cow_http2_machine.erl cow_http2_machine:headers_decode allocation of resources

Summaryinfo

A vulnerability marked as problematic has been reported in ninenines cowlib. This affects the function cow_http2_machine:headers_decode of the file src/cow_http2_machine.erl of the component HPACK Decoder. The manipulation leads to allocation of resources. This vulnerability is listed as CVE-2026-113431. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in ninenines cowlib (the affected version is unknown). This issue affects the function cow_http2_machine:headers_decode of the file src/cow_http2_machine.erl of the component HPACK Decoder. The manipulation with an unknown input leads to a allocation of resources vulnerability. Using CWE to declare the problem leads to CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. Impacted is availability. The summary by CVE is:

Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowlib allows an unauthenticated remote peer to exhaust the memory of an HTTP/2 endpoint via HPACK-indexed header fields. cow_http2_machine:headers_decode/4 in src/cow_http2_machine.erl decodes every HEADERS block with cow_hpack:decode/3. It bounds the compressed block size and the number of fields, but not the size of the decoded header list that RFC 9113 section 6.5.2 places under SETTINGS_MAX_HEADER_LIST_SIZE. A peer stores one header value of up to the dynamic table size (4096 bytes by default) and then references it with one-byte indexed fields, so about 100 bytes on the wire decode to a header list of about 390 KB. A consumer that copies the decoded values, as Cowboy does when cowboy_http2:headers_to_map/2 joins repeated cookie fields into one binary, allocates that amount for every stream. The total across streams and connections is not bounded. This issue affects cowlib: from 2.7.0 onward.

The advisory is shared at cna.erlef.org. The identification of this vulnerability is CVE-2026-113431 since 10/30/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Vendor

• ninenines

Name

• cowlib

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• 🔒

CPE 2.2info

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