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

High · CVSS 8.2CVE-2026-91043

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

Answer in brief

CVE-2026-91043 records a High severity (CVSS 8.2) vulnerability in HPACK-indexed cookie fields in Mint HTTP/2 responses bypass max_header_list_size and exhaust client memory. The current sources do not mark it as known exploited. The current feed maps elixir-mint/elixir-mint/mint (generic), elixir-mint/mint (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 28, 2026Updated Sep 28, 2026Source checked Sep 28, 2026First seen by HOL Sep 28, 2026Material review Sep 28, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 8.2
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 8.2. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps elixir-mint/elixir-mint/mint (generic), elixir-mint/mint (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
elixir-mint/elixir-mint/mintgeneric	>=8e0e04680476f90f9f68db4dfeabcbe66dabfc4d <c7895cb022196c77ec35570c8e873a84393ff4b8	c7895cb022196c77ec35570c8e873a84393ff4b8
elixir-mint/mintgeneric	>=1.1.0 <1.11.0	1.11.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for elixir-mint/elixir-mint/mint, elixir-mint/mint.
Review the reported fix. Source-reported 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.

Evidence timeline and material changes

Published upstream
Sep 28, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 28, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 28, 2026

Sources and claim methodology

Upstream source 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 1.11.0.

Quoted source text, attributed separately from HOL analysis.