---
cve: "CVE-2026-39804"
severity: "HIGH"
cvss: 8.2
epss: "63%"
vendor: "mtrudel"
kev: false
exploited: false
published: "2026-05-01 21:16:16"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-09-10T09:20:45+02:00"
---

# CVE-2026-39804

> 8.2 HIGH · 🧪 PoC

## Beschreibung

Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion when WebSocket permessage-deflate compression is enabled.

'Elixir.Bandit.WebSocket.PerMessageDeflate':inflate/2 in lib/bandit/websocket/permessage_deflate.ex calls :zlib.inflate/2 with no output-size cap, then materializes the entire decompressed payload as a single binary via IO.iodata_to_binary/1. The websocket_options.max_frame_size option only bounds the on-the-wire (compressed) frame size, not the decompressed output. A high-ratio compressed frame (e.g. uniform data at ~1024:1 ratio) can stay well under any wire-size limit while forcing GiB-scale heap allocations in the connection process before any application code runs.

An unauthenticated attacker who can open a WebSocket connection can send a single such frame to exhaust the BEAM node's memory and trigger an OOM kill.

This vulnerability requires both Bandit's server-level websocket_options.compress and the per-upgrade compress: true option passed to WebSockAdapter.upgrade/4 to be enabled. Stock Phoenix and LiveView applications are not affected as they default to compress: false.

This issue affects bandit: from 0.5.9 before 1.11.0.

## CVSS-Vektor

```
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |

## Patch verfügbar (OSV)

- e62619895d0d2584d7ffa57d43ef6f72437dfaff (Commit)
- 8156921a51e684a951221da7bc30a70a022f722e (Commit)

## Referenzen

- <https://github.com/mtrudel/bandit/security/advisories/GHSA-frh3-6pv6-rc8j>
- <https://cna.erlef.org/cves/CVE-2026-39804.html>
- <https://osv.dev/vulnerability/EEF-CVE-2026-39804>
- <https://github.com/mtrudel/bandit/commit/8156921a51e684a951221da7bc30a70a022f722e>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-39804) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_