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

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.

Scores

EPSS (exploitation in 30 days)

0.42% · top 63% of all CVEs (6 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.2.

Weakness

• CWE-770 Allocation of Resources Without Limits or Throttling (opens in a new tab)All about CWE-770 and its CVEs

Affected products

• elixir-mint · mint

  • affected 1.1.0 – < 1.10.2

• elixir-mint · mint

  • affected 8e0e04680476f90f9f68db4dfeabcbe66dabfc4d – < *

What to do

Workaround: Lower client_settings: [max_header_list_size: n] in Mint.HTTP.connect/4. The compressed check still applies, and each byte of the block can expand to at most one 4 KB table entry, so a limit of 4,096 bounds a response to roughly 16 MB. Alternatively, restrict connections to untrusted servers to HTTP/1 with protocols: [:http1], which avoids the HTTP/2 receive path entirely. Do not set max_header_list_size: :infinity, which disables the compressed check as well.

References (6)

• GitHub Advisory (opens in a new tab)relatedvendor-advisory
• EEF CNA record for CVE-2026-91043 (opens in a new tab)related
• OSV record EEF-CVE-2026-91043 (opens in a new tab)related
• Introducing commit 8e0e046 in elixir-mint/mint (opens in a new tab)related
• Fix commit c7895cb in elixir-mint/mint (opens in a new tab)patch
• Fix commit 65a0d61 in elixir-mint/mint (opens in a new tab)patch

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-91043](https://trackcve.app/badge/CVE-2026-91043.svg)](https://trackcve.app/cve/CVE-2026-91043)

Record last updated 29 Sept 2026, 10:15 UTC.