What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 8.2 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-28 · updated 2026-09-29
• Weakness: CWE-770

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.

Affected products

• elixir-mint mint: from 1.1.0 before 1.10.2 — fixed in 1.10.2

How to fix

Upgrade to a fixed version: elixir-mint mint 1.10.2. Check the vendor advisory for mitigations.

References

• https://cna.erlef.org/cves/CVE-2026-91043.html
• https://github.com/elixir-mint/mint/commit/65a0d61c9eab6b0dedac809de7212515bf506250
• https://github.com/elixir-mint/mint/commit/8e0e04680476f90f9f68db4dfeabcbe66dabfc4d
• https://github.com/elixir-mint/mint/commit/c7895cb022196c77ec35570c8e873a84393ff4b8
• https://github.com/elixir-mint/mint/security/advisories/GHSA-9x8p-qrf4-jq7g
• https://osv.dev/vulnerability/EEF-CVE-2026-91043

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