Is CVE-2026-113431 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-113431 being exploited in the wild.

How severe is CVE-2026-113431?

Informational severity, published 6 November 2026.

Which products and versions are affected?

Ninenines Cowlib 2.7.0 and later.

Is there a fix for CVE-2026-113431?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-113431 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-113431?

Check whether you run Ninenines Cowlib at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-113431: ninenines cowlib unbounded memory allocation via HPACK headers

CVE-2026-113431 · Severity: info · Published 2026-11-06

cowlib is a library used by Cowboy web server to handle HTTP/2 protocol communication. An unauthenticated attacker can send specially crafted HTTP/2 headers that force the server to allocate excessive memory, potentially causing denial of service. By referencing large header values multiple times across streams, an attacker can exhaust available memory and crash the service without authentication or user interaction.

Vendors: Ninenines.

Quick answers

Is CVE-2026-113431 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-113431 being exploited in the wild.
How severe is CVE-2026-113431?: Informational severity, published 6 November 2026.
Which products and versions are affected?: Ninenines Cowlib 2.7.0 and later.
Is there a fix for CVE-2026-113431?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-113431 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-113431?: Check whether you run Ninenines Cowlib at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability exists in cow_http2_machine:headers_decode/4, which decodes HPACK-indexed headers without enforcing RFC 9113's SETTINGS_MAX_HEADER_LIST_SIZE limit on the decoded output size. An attacker can craft a small compressed payload (around 100 bytes) that expands to 390 KB of decoded headers by storing one large dynamic table value and repeatedly referencing it with single-byte indexed fields. When applications copy decoded header values, memory allocation compounds across multiple streams and connections without bounds.

Affected products

ninenines cowlib 2.7.0 and later

Timeline

2026-11-06: disclosed

References

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