HPACK-indexed cookie fields in Mint HTTP/2 responses bypass max_header_list_size and exhaust client memory
Published Sep 28, 2026
8.2
HIGHCVSS 4.0
EPSS 0.42%
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
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- Version 1.1.0StatusaffectedConstraints<1.10.2
- Version
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- Version StatusaffectedConstraints<*
- Version
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Elixir-Mint | Mint | unaffected |
| ||||||
| Elixir-Mint | Mint | unaffected |
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No data.
No data.
No Red Hat product state for this CVE.
No package ranges for this CVE.
Remediation
Vendor solution
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 (7)
- https://cna.erlef.org/cves/CVE-2026-91043.html related
- https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-88218 Advisory
- https://github.com/elixir-mint/mint/commit/65a0d61c9eab6b0dedac809de7212515bf506250 patch
- https://github.com/elixir-mint/mint/commit/8e0e04680476f90f9f68db4dfeabcbe66dabfc4d related
- https://github.com/elixir-mint/mint/commit/c7895cb022196c77ec35570c8e873a84393ff4b8 patch
- https://github.com/elixir-mint/mint/security/advisories/GHSA-9x8p-qrf4-jq7g relatedvendor-advisory
- https://osv.dev/vulnerability/EEF-CVE-2026-91043 related
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