---
cve: "CVE-2026-39803"
severity: "HIGH"
cvss: 8.7
epss: "64%"
vendor: "mtrudel"
kev: false
exploited: false
published: "2026-05-13 14:17:32"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-09-10T09:09:03+02:00"
---

# CVE-2026-39803

> 8.7 HIGH · 🧪 PoC

## Beschreibung

Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated remote denial of service via memory exhaustion.

The chunked clause of 'Elixir.Bandit.HTTP1.Socket':read_data/2 in lib/bandit/http1/socket.ex ignores the caller-supplied :length option when reading HTTP/1 chunked request bodies. Instead of capping the accumulated body at the configured limit (e.g. Plug.Parsers' default 8 MB), do_read_chunked_data!/5 buffers every received chunk into an iolist unconditionally and materializes the entire body as a single binary. The function always returns {:ok, body, ...}, so callers cannot interpose a 413 response.

Because Plug.Parsers runs before routing and authentication in the standard Phoenix endpoint, an unauthenticated attacker needs no valid route or credentials. Sending a single Transfer-Encoding: chunked POST request with an arbitrarily large body to any path causes the BEAM process to exhaust available memory and be terminated by the OS OOM killer.

The content-length path in the same function correctly enforces the limit and is not affected.

This issue affects bandit: from 1.4.0 before 1.11.1.

## CVSS-Vektor

```
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
```

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

## Patch verfügbar (OSV)

- 40a1b8fc924694a0125bbaa7fee101fa43feeb52 (Commit)
- ae3520dfdbfab115c638f8c7f6f6b805db34e1ab (Commit)

## Referenzen

- <https://github.com/mtrudel/bandit/security/advisories/GHSA-9q9q-324x-93r2>
- <https://cna.erlef.org/cves/CVE-2026-39803.html>
- <https://osv.dev/vulnerability/EEF-CVE-2026-39803>
- <https://github.com/mtrudel/bandit/commit/ae3520dfdbfab115c638f8c7f6f6b805db34e1ab>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-39803) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_