CVE-2026-109584
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.
How to fix
- mtrudel bandit1.14.0, 220b9dfd27f9a21305be2afc75cbe585ddc24e7a or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mtrudel bandit | 0.3.3 ≤ v < 1.14.0, 44bf969cd59851622fb6ee4d16227fbc39a77fb4 ≤ v < 220b9dfd27f9a21305be2afc75cbe585ddc24e7a | 1.14.0, 220b9dfd27f9a21305be2afc75cbe585ddc24e7a |
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