High severity · published May 13, 2026
CVE-2026-39806
HTTP/1 chunked decoder infinite loop on requests with trailer fields in bandit
7.5
CVSS
0.6%
EPSS
No
On KEV
Description
Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in mtrudel bandit allows unauthenticated remote denial of service via worker process exhaustion.
'Elixir.Bandit.HTTP1.Socket':do_read_chunked_data!/5 in lib/bandit/http1/socket.ex terminates only when the last-chunk line 0\r\n is followed immediately by the empty trailer line \r\n. RFC 9112 §7.1.2 permits zero or more trailer fields between them. When trailers are present, none of the match clauses fit: the catch-all arm computes a negative to_read, calls read_available!/2, receives <<>> on timeout, and tail-recurses with unchanged state. The worker process is pinned for the lifetime of the TCP connection.
A handful of concurrent connections sending RFC-conformant chunked requests with trailer fields is sufficient to exhaust the Bandit worker pool and render the server unresponsive to all further traffic. No authentication, special headers, or large payload is required. Proxies such as NGINX and HAProxy legitimately forward trailer-bearing requests, so servers behind such proxies may be affected without any malicious client involvement.
This issue affects bandit: from 1.6.1 before 1.11.1.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.6% · higher than 50% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
BA
bandit · mtrudel
1.6.1 before 1.11.1; e73e379ab59840e8561b5730878f16e29ab06217 before ae3520dfdbfab115c638f8c7f6f6b805db34e1ab · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-39806
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-39806
Third Party Advisory
https://cna.erlef.org/cves/CVE-2026-39806.html
Patch
https://github.com/mtrudel/bandit/commit/ae3520dfdbfab115c638f8c7f6f6b805db34e1ab
Exploit
https://github.com/mtrudel/bandit/security/advisories/GHSA-rf5q-vwxw-gmrf
Third Party Advisory
https://osv.dev/vulnerability/EEF-CVE-2026-39806
More from bandit
8.7
CVE-2026-116078
HTTP/2 request bodies made of 1-byte DATA frames amplify memory use in Bandit
8.7
CVE-2026-108529
SETTINGS and stream-0 WINDOW_UPDATE frames trigger quadratic work over blocked streams in Bandit
8.7
CVE-2026-110499
Client-chosen HPACK encoder table size is applied uncapped, growing per-connection state with every response in Bandit
8.7
CVE-2026-109584
HTTP/2 cookie crumb join expands a small HPACK header block into an unbounded allocation in Bandit
8.7
CVE-2026-111101
HTTP/1.1 chunked request bodies made of 1-byte chunks amplify memory use in Bandit
