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Back to active CVEs
High · CVSS 8.7CVE-2026-109584

HTTP/2 cookie crumb join expands a small HPACK header block into an unbounded allocation in BanditCVE-2026-109584

Answer in brief

CVE-2026-109584 records a High severity (CVSS 8.7) vulnerability in HTTP/2 cookie crumb join expands a small HPACK header block into an unbounded allocation in Bandit. The current sources do not mark it as known exploited. The current feed maps mtrudel/bandit (generic), mtrudel/mtrudel/bandit (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 Oct 26, 2026Updated Oct 26, 2026Source checked Oct 26, 2026First seen by HOL Oct 26, 2026Material review Oct 26, 2026
Upstream Advisory

Key facts

Risk
High · CVSS 8.7
Exploitation
Not marked as known exploited
Affected software
2 mapped packages or products
Fix availability
Available

Why this deserves its current priority

CVSS is 8.7. 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 mtrudel/bandit (generic), mtrudel/mtrudel/bandit (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
PackageAffected rangeFixed version
mtrudel/banditgeneric>=0.3.3 <1.14.01.14.0
mtrudel/mtrudel/banditgeneric>=44bf969cd59851622fb6ee4d16227fbc39a77fb4 <220b9dfd27f9a21305be2afc75cbe585ddc24e7a220b9dfd27f9a21305be2afc75cbe585ddc24e7a

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for mtrudel/bandit, mtrudel/mtrudel/bandit.
  2. 2Review the reported fix. Source-reported workaround: On 1.12.2 and later, set a finite decoded header list limit, for example http_2_options: [default_local_settings: [max_header_list_size: 65_536]], which resets the stream before the cookie crumbs are joined. From 0.7.0, disabling HTTP/2 with http_2_options: [enabled: false] removes the vulnerable path.

Evidence timeline and material changes

  1. Published upstream

    Oct 26, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Oct 26, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Oct 26, 2026

Sources and claim methodology

  • Source referencecna.erlef.org
  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
  • Source referenceosv.dev
Upstream source description

Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in the HTTP/2 implementation of mtrudel bandit allows an unauthenticated remote attacker to exhaust server memory via a small HPACK-compressed HEADERS block. The block stores one large cookie value in the HPACK dynamic table and then references it tens of thousands of times with 1-byte indexed fields. In the reporter's run, a 49 KB block made a server with default settings allocate a 183 MB cookie binary before any application code ran, and every concurrent stream can repeat the cost. Bandit.HTTP2.Connection caps only the compressed block (max_header_block_size), and its check of the decoded list against max_header_list_size never fires because that setting defaults to :infinity. combine_cookie_crumbs/1 in lib/bandit/http2/stream.ex then joins every crumb into one binary. This issue affects bandit: from 0.3.3 before 1.14.0.

Quoted source text, attributed separately from HOL analysis.

Related CVEs

  • Unbounded memory consumption during PDF text extractionAlso CWE-409

Record context

Vulnerability class
Missing Auth
EPSS
Not reported
CWE IDs
CWE-409
Source
CVE List V5
Source checked
Oct 26, 2026
References
5 linked sources
Open source record