WebSocket fragmented message reassembly unbounded in bandit
Summary
| CVE | CVE-2026-42786 |
|---|---|
| State | PUBLISHED |
| Assigner | EEF |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-05-01 21:16:17 UTC |
| Updated | 2026-05-02 02:16:00 UTC |
| Description | Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion. The fragment reassembly path in 'Elixir.Bandit.WebSocket.Connection':handle_frame/3 in lib/bandit/websocket/connection.ex appends every incoming Continuation{fin: false} frame's payload to a per-connection iolist with no cumulative size cap. The existing max_frame_size option only bounds individual frames; a peer that streams an unbounded number of continuation frames without ever setting fin=1 grows BEAM heap linearly until the OS or a supervisor kills the process. Because the accumulation happens before WebSock.handle_in/2 is called, the application has no opportunity to interpose a size check. Phoenix Channels and LiveView both run over WebSock on Bandit, so a stock Phoenix application exposes this surface as soon as it accepts socket connections. This issue affects bandit: from 0.5.0 before 1.11.0. |
Risk And Classification
Primary CVSS: v4.0 8.7 HIGH from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Problem Types: CWE-770 | CWE-770 CWE-770 Allocation of Resources Without Limits or Throttling
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | Secondary | 8.7 | HIGH | 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/E:X/C... |
| 4.0 | CNA | CVSS | 8.7 | HIGH | 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 |
CVSS v4.0 Breakdown
Attack Vector
NetworkAttack Complexity
LowAttack Requirements
NonePrivileges Required
NoneUser Interaction
NoneConfidentiality
NoneIntegrity
NoneAvailability
HighSub Conf.
NoneSub Integrity
NoneSub Availability
NoneCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Vendor Declared Affected Products
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/mtrudel/bandit/commit/21612c7c7b1ce43eccd36d3af3a2299d23513667 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | |
| osv.dev/vulnerability/EEF-CVE-2026-42786 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | osv.dev | |
| github.com/mtrudel/bandit/security/advisories/GHSA-pf94-94m9-536p | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | github.com | |
| cna.erlef.org/cves/CVE-2026-42786.html | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | cna.erlef.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Peter Ullrich (en)
CNA: Mat Trudel (en)
CNA: Jonatan Männchen (en)
There are currently no legacy QID mappings associated with this CVE.