EEF-CVE-2026-39804

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Source

https://cna.erlef.org/osv/EEF-CVE-2026-39804.html

Import Source

https://cna.erlef.org/osv/EEF-CVE-2026-39804.json

JSON Data

https://api.osv.dev/v1/vulns/EEF-CVE-2026-39804

Aliases

CVE-2026-39804
GHSA-frh3-6pv6-rc8j

Published

2026-05-01T20:34:24.604Z

Modified

2026-05-02T04:17:35.717Z

Severity

8.2 (High) CVSS_V4 - 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 CVSS Calculator

Summary

WebSocket permessage-deflate inflate has no output-size cap in bandit

Details

Summary

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/permessagedeflate.ex calls :zlib.inflate/2 with no output-size cap, then materializes the entire decompressed payload as a single binary via IO.iodatatobinary/1. The websocketoptions.maxframesize 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.

Workaround

Do not pass compress: true to WebSockAdapter.upgrade/4. Omitting this option (or setting it to false) prevents permessage-deflate from being negotiated, so the inflate path is never reached.

Configuration

The vulnerability is only reachable when both of the following conditions are true: - Bandit's server-level websocket_options.compress is enabled (it defaults to true). - The per-upgrade compress: true option is passed to WebSockAdapter.upgrade/4 (it defaults to false; Phoenix's default is also false).

Stock Phoenix and LiveView applications are not affected because compress: false is their default.

Database specific

{
    "cpe_ids": [
        "cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"
    ],
    "capec_ids": [
        "CAPEC-130"
    ],
    "cwe_ids": [
        "CWE-770"
    ]
}

References

Credits

- Peter Ullrich - FINDER

Affected packages

Hex / bandit

Package

Name: bandit
Purl: pkg:hex/bandit

Affected ranges

Type: SEMVER
Events: Introduced

0.5.9

Fixed

1.11.0

Affected versions

0.*

0.5.9

0.5.10

0.5.11

0.6.0

0.6.1

0.6.2

0.6.3

0.6.4

0.6.5

0.6.6

0.6.7

0.6.8

0.6.9

0.6.10

0.6.11

0.7.0

0.7.1

0.7.2

0.7.3

0.7.4

0.7.5

0.7.6

0.7.7

1.*

1.0.0-pre.1

1.0.0-pre.2

1.0.0-pre.3

1.0.0-pre.4

1.0.0-pre.5

1.0.0-pre.6

1.0.0-pre.7

1.0.0-pre.8

1.0.0-pre.9

1.0.0-pre.10

1.0.0-pre.11

1.0.0-pre.12

1.0.0-pre.13

1.0.0-pre.14

1.0.0-pre.15

1.0.0-pre.16

1.0.0-pre.17

1.0.0-pre.18

1.0.0

1.1.0

1.1.1

1.1.2

1.1.3

1.2.0

1.2.1

1.2.2

1.2.3

1.3.0

1.4.0

1.4.1

1.4.2

1.5.0

1.5.1

1.5.2

1.5.3

1.5.4

1.5.5

1.5.6

1.5.7

1.6.0

1.6.1

1.6.2

1.6.3

1.6.4

1.6.5

1.6.6

1.6.7

1.6.8

1.6.9

1.6.10

1.6.11

1.7.0

1.8.0

1.9.0

1.10.0

1.10.1

1.10.2

1.10.3

1.10.4

Database specific

source

"https://cna.erlef.org/osv/EEF-CVE-2026-39804.json"

Git / github.com/mtrudel/bandit

Affected ranges

Type: GIT
Repo: https://github.com/mtrudel/bandit
Events: Introduced

da4027cff7d2b80319e76fe7a32f84beceec490a

Fixed

1.11.0

Database specific

source

"https://cna.erlef.org/osv/EEF-CVE-2026-39804.json"