CVE-2026-114213

WebSocket 1-byte continuation frames bypass `max_fragmented_message_size` in Bandit

Published Oct 26, 2026 CVSS 4.0 · 8.7 High EPSS < 1% KEV · Not listed

Description

Allocation of Resources Without Limits or Throttling vulnerability in the WebSocket fragment reassembly of mtrudel bandit allows an unauthenticated remote attacker to exhaust server memory via a fragmented message made of many 1-byte continuation frames.

Bandit.WebSocket.Connection checks max_fragmented_message_size against the payload bytes received, but keeps every non-final continuation frame as a new list cell around its own binary, and nothing limits the number of fragments. A 1-byte fragment costs 7 bytes on the wire but about 150 to 170 bytes of server memory, so one connection can hold about 150 times the configured limit, roughly 1.2 to 1.4 GB at the default 8 MB. Ping frames between fragments keep the connection alive past the idle timeout.

This issue affects bandit: from 1.11.0 before 1.14.0.

Analysis

Technical impact

The vulnerability is an allocation of resources without limits or throttling in the WebSocket fragment reassembly of Bandit. An unauthenticated remote attacker can send a fragmented message composed of many 1‑byte continuation frames. Each 1‑byte fragment consumes roughly 150‑170 bytes of server memory, allowing an attacker to exhaust up to about 1.2–1.4 GB per connection on the default 8 MB limit, potentially causing a denial of service.

Affected Systems

Bandit (mtrudel:bandit) versions 1.11.0 through 1.13.9 are affected. The issue does not exist in 1.14.0 or newer.

Risk and Exploitability

The CVSS score is 8.7, indicating a high severity. EPSS is not available and the vulnerability is not listed in CISA’s Known Exploited Vulnerabilities catalog. The attack vector is an unauthenticated remote connection to a WebSocket endpoint, where the attacker sends many 1‑byte continuation frames that bypass the max_fragmented_message_size check. The default logic stores each non‑final continuation frame in a separate list cell, so an attacker can consume server memory with a single persistent connection and may crash or degrade the service.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

mtrudel

bandit

unaffected

Version	Status	Constraints
`1.11.0`	affected	< 1.14.0

mtrudel

bandit

unaffected

Version	Status	Constraints
`21612c7c7b1ce43eccd36d3af3a2299d23513667`	affected	< 220b9dfd27f9a21305be2afc75cbe585ddc24e7a

No data.

Vendor Product Versions

Mtrudel

Bandit

Version	Status	Scheme	Platform
`[1.11.0,1.14.0)`	affected	semver	—

Mtrudel

Bandit

Version	Status	Scheme	Platform
`[21612c7c7b1ce43eccd36d3af3a2299d23513667,220b9dfd27f9a21305be2afc75cbe585ddc24e7a)`	affected	code_commit	—

Remediation

Vendor Workaround

Lower websocket_options: [max_fragmented_message_size: ...] to the largest fragmented message the application needs, for example 65_536. Memory per connection stays at about 150 times this limit, so a lower limit lowers the ceiling.

OpenCVE Recommended Actions

Upgrade to Bandit version 1.14.0 or newer
Configure websocket_options.max_fragmented_message_size to a lower value, such as 65536 bytes
Limit or rate‑limit connections to the WebSocket endpoint to mitigate potential denial‑of‑service attacks

Generated by OpenCVE AI on October 26, 2026 at 15:24 UTC.

Tracking

Advisories

No advisories available

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact None

Vulnerable System Availability Impact High

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

No CVSS v3.1

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.602% probability within 30 days)

Exploitation none

Automatable yes

Technical Impact partial

References

Link	Providers
https://cna.erlef.org/cves/CVE-2026-114213.html
https://github.com/mtrudel/bandit/commit/21612c7c7b1ce43eccd36d3af3a2299d23513667
https://github.com/mtrudel/bandit/commit/220b9dfd27f9a21305be2afc75cbe585ddc24e7a
https://github.com/mtrudel/bandit/security/advisories/GHSA-cpx7-qf6w-jc63
https://osv.dev/vulnerability/EEF-CVE-2026-114213

History

Oct 26, 2026 4:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Oct 26, 2026 2:00 PM Description updated. Title updated. First appearance in the feed. Weaknesses updated. Affected versions updated. Affected vendors updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
Description		Allocation of Resources Without Limits or Throttling vulnerability in the WebSocket fragment reassembly of mtrudel bandit allows an unauthenticated remote attacker to exhaust server memory via a fragmented message made of many 1-byte continuation frames. Bandit.WebSocket.Connection checks max_fragmented_message_size against the payload bytes received, but keeps every non-final continuation frame as a new list cell around its own binary, and nothing limits the number of fragments. A 1-byte fragment costs 7 bytes on the wire but about 150 to 170 bytes of server memory, so one connection can hold about 150 times the configured limit, roughly 1.2 to 1.4 GB at the default 8 MB. Ping frames between fragments keep the connection alive past the idle timeout. This issue affects bandit: from 1.11.0 before 1.14.0.
Title		WebSocket 1-byte continuation frames bypass `max_fragmented_message_size` in Bandit
First Time appeared		Mtrudel Mtrudel bandit
Weaknesses		CWE-770
CPEs		cpe:2.3:a:mtrudel:bandit::::::::
Vendors & Products		Mtrudel Mtrudel bandit
References		https://cna.erlef.org/cves/CVE-2026-114213.html https://github.com/mtrudel/bandit/commit/21612c7c7b1ce43eccd36d3af3a2299d23513667 https://github.com/mtrudel/bandit/commit/220b9dfd27f9a21305be2afc75cbe585ddc24e7a https://github.com/mtrudel/bandit/security/advisories/GHSA-cpx7-qf6w-jc63 https://osv.dev/vulnerability/EEF-CVE-2026-114213
Metrics		cvssV4_0 `{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}`