Allocation of Resources Without Limits or Throttling vulnerability in ninenines cowlib allows an…

Why it is Yellow

• CVSS 8.7 high
• Remotely exploitable without logging in

References

• https://cna.erlef.org/cves/CVE-2026-113431.html
• https://github.com/ninenines/cowlib/commit/a3b15e29b3067644bfd580246c87f7af7a90b3b8
• https://github.com/ninenines/cowlib/commit/b461b119e78e4e09bb28b186b09da7ed4a86a0dd
• https://osv.dev/vulnerability/EEF-CVE-2026-113431

Original description

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.