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🛡️ CVE-2026-65623 — bandit

⚪ Unknown ✅ No Known Exploit CWE-407 NVD
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Quadratic CPU blow-up reassembling fragmented WebSocket messages in Bandit

Summary

Inefficient Algorithmic Complexity vulnerability in mtrudel bandit allows unauthenticated remote denial of service via CPU exhaustion during WebSocket fragment reassembly.

The size guard 'Elixir.Bandit.WebSocket.Connection':oversize\_message?/2 called from handle\_frame/3 in lib/bandit/websocket/connection.ex appends each non-final continuation frame to a left-nested iolist and then re-measures the entire accumulated buffer with IO.iodata\_length/1 on every frame. Because the buffer grows by one element per frame and is fully re-traversed each time, reassembly work is quadratic (O(n^2)) in the number of continuation frames.

The max\_fragmented\_message\_size limit (default 8 MB) bounds total bytes but not frame count, and each frame can carry as little as one payload byte, so an attacker can send millions of tiny continuation frames using modest bandwidth to pin a CPU core for minutes to hours. Many concurrent connections can starve the whole server of CPU, denying service to legitimate users. The WebSocket read timeout does not help, because it is an idle timeout evaluated between reads and cannot preempt the synchronous reassembly work spent inside a single callback.

This issue affects bandit: from 1.11.0 before 1.12.1.

Configuration

This vulnerability only affects applications that serve WebSocket endpoints through Bandit (including Phoenix applications that use Bandit as the HTTP adapter). Applications that do not upgrade any connections to WebSocket are not affected.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this 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

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Attack requirements: None — no deployment-specific condition has to hold.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-65623 is classified as CWE-407: Inefficient Algorithmic Complexity. Crafted input drives an algorithm into its worst case, so a small request costs disproportionate work.

Affected software

CVE-2026-65623 is recorded against 2 packages.

  • bandit
  • unknown

Timeline and source

Published on 24 July 2026 and last revised on 30 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

github.com (Advisory)
cna.erlef.org (Web)
github.com (Fix)
hex.pm (Package)

Other advisories for this package

bandit has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-407: Inefficient Algorithmic Complexity) in other software:

Details

Severity Unknown
CVSS Score N/A
CVSS 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
CWE CWE-407
Public Exploit ✅ No
Source NVD
Published 2026-07-24
Updated 2026-08-20
Modified 2026-07-30

Affected Packages

Software From version Fixed in
bandit — —
unknown — —

Similar Threats

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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