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.
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Affected Vendors & Products
References
History
Fri, 06 Nov 2026 10:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | Unbounded decoded HTTP/2 header-list size in cowlib cow_http2_machine enables HPACK amplification memory exhaustion | |
| First Time appeared |
Ninenines
Ninenines cowlib |
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| Weaknesses | CWE-770 | |
| CPEs | cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Ninenines
Ninenines cowlib |
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| References |
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| Metrics |
cvssV4_0
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Status: PUBLISHED
Assigner: EEF
Published: 2026-11-06T10:28:15.837Z
Updated: 2026-11-06T10:28:15.837Z
Reserved: 2026-10-30T12:30:02.006Z
Link: CVE-2026-113431
No data.
Status : Received
Published: 2026-11-06T11:17:04.410
Modified: 2026-11-06T11:17:04.410
Link: CVE-2026-113431
No data.
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