CVE-2026-91043 HPACK-indexed cookie fields in Mint HTTP/2 responses bypass max_header_list_size and exhaust client memory

What is CVE-2026-91043?

CVE-2026-91043 is a high-severity denial of service vulnerability in elixir-mint mint, published on 28 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Allocation of Resources Without Limits or Throttling vulnerability in elixir-mint mint allows a malicious HTTP/2 server to exhaust memory on the client host and cause a denial of service.

Mint.HTTP2 enforces the client's max_header_list_size setting only on the compressed size of an inbound header block, while RFC 9113 section 6.5.2 defines the limit on the decoded header list. An HPACK indexed field costs one byte on the wire and decodes to a dynamic table entry of up to 4 KB, and join_cookie_headers/1 in lib/mint/http2.ex copies every cookie value of a response into one new binary. A header block under the default 256 KB wire limit therefore makes the client allocate about 1 GB for a single response, and several such responses in one delivery exhaust the memory of the process that owns the connection or of the whole VM.

This issue affects mint: from 1.1.0 before 1.10.2.

Weakness: CWE-770

Which versions are affected by CVE-2026-91043?

1 open source package ship an affected version, including mint.

How do I fix CVE-2026-91043?

Upgrade mint to 1.10.2 or later.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-91043 being exploited?

There is no known exploitation of CVE-2026-91043 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as EEF-CVE-2026-91043, GHSA-9x8p-qrf4-jq7g.