CVE-2026-110499: Client-chosen HPACK encoder table size is applied uncapped, growing per-connection state with every response in Bandit

Severity: high (CVSS 8.7 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-26 · updated 2026-10-26
Weakness: CWE-770

Description

Allocation of Resources Without Limits or Throttling vulnerability in the HTTP/2 implementation of mtrudel bandit allows an unauthenticated remote attacker to grow per-connection memory and CPU cost without bound via a large SETTINGS_HEADER_TABLE_SIZE. Bandit resizes its HPACK encoder table to whatever size the client advertises, up to 2^32-1 bytes, and indexes response headers into it. Because responses carry distinct values such as date or content-length, nothing is evicted and the table grows with every response for the life of the connection, while each lookup scans it linearly. The SETTINGS handling in Bandit.HTTP2.Connection (lib/bandit/http2/connection.ex) passes remote_settings.header_table_size to HPAX.resize/2 with no server-side cap, and encode_headers encodes every response header as :store. Serving N responses on one connection therefore costs O(N²) CPU in the connection process. This issue affects bandit: from 0.3.6 before 1.14.0.

Affected products

mtrudel bandit: from 0.3.6 before 1.14.0 — fixed in 1.14.0

How to fix

Upgrade to a fixed version: mtrudel bandit 1.14.0. Check the vendor advisory for mitigations.

References

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