Memory exhaustion via small HPACK headers in Bandit HTTP/2 server
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- None
- Impact type
- —
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Fixed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA.
Summary
The mtrudel bandit package from 0.3.3 before 1.14.0 is affected. Its HTTP/2 implementation mishandles highly compressed data (CWE-409), so a small HPACK compressed header block expands into a very large cookie allocation. An unauthenticated remote attacker can exhaust server memory, and concurrent streams can repeat the cost.
Written with Claude Haiku 5.5 from the sources below · 2026-11-06
Description from the CNA
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
Remediation
Upgrade bandit to version 1.14.0, which contains the fix.
Written with Claude Haiku 5.5 from the sources below · 2026-11-06
- Fix · CNA bandit (mtrudel) Fixed in 1.14.0
Fixed in the same release
Records fixed by the same vendor advisory or release, as the CNA lists them.
- Release ·
mtrudel bandit 1.14.0, 220b9dfd27f9a21305be2afc75cbe585ddc24e7a
11 records Highest priority Priority MEDIUM 10 MEDIUM, 1 LOW
Other records, highest priority first
- TI-2026-80361 Bandit frames still reach WebSock after server-initiated closePriority MEDIUM 61
- TI-2026-80382 HTTP/2 frames let clients hold Bandit request body reads openPriority MEDIUM 45
- TI-2026-80371 WebSocket 1-byte continuation frames exhaust memory in BanditPriority MEDIUM 45
Timeline
- 2026-10-26 Threatist record created from CVE-2026-109584
- 2026-10-26 CISA SSVC decision points changed
References
More mtrudel vulnerabilities
- TI-2026-81989 HTTP/2 request bodies made of 1-byte DATA frames amplify memory use in Bandit CVSS 4.0HIGH 8.7
- TI-2026-74311 Bandit HTTP/2 send timers reset, letting trickles pin stream processes CVSS 4.0HIGH 8.7
- TI-2026-52571 HTTP/2 connection-window starvation pins Plug processes indefinitely in Bandit CVSS 4.0HIGH 8.7
- TI-2026-46780 Quadratic CPU blow-up reassembling fragmented WebSocket messages in Bandit CVSS 4.0HIGH 8.7
- TI-2026-31007 WebSocket fragmented message reassembly unbounded in bandit CVSS 4.0HIGH 8.7
- TI-2026-28689 HTTP/1 chunked decoder infinite loop on requests with trailer fields in bandit CVSS 4.0HIGH 8.7
Sources
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences