CVE-2026-109584

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

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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.

CVSS 8.7 · Élevée · EPSS 0,6% · Correctif disponible

Publication

2026-10-26T13:32:22.359Z

Mise à jour

2026-10-26T15:35:51.081Z

Pile logicielle: system

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