CVE-2026-77528Public exploitNetwork attack vector

Unauthenticated resource exhaustion via unchecked decompression

Published Sep 18, 2026 · Updated Sep 18, 2026

Improper compressed-data handling in Autobahn|Python before 26.7.1 allows remote attackers to exhaust resources via WebSocket frames. The receive path checks maxMessagePayloadSize against compressed length, inflates without an output cap, and delivers oversized data to callbacks. Exploitation requires an endpoint that accepts permessage-deflate and relies on that limit; the demonstrated consequence is availability loss through excess allocation and processing.

CVSS severity5.3
Medium
EPSS probability0.52%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper compressed-data handling in Autobahn|Python before 26.7.1 allows remote attackers to exhaust resources via WebSocket frames. The receive path checks maxMessagePayloadSize against compressed length, inflates without an output cap, and delivers oversized data to callbacks. Exploitation requires an endpoint that accepts permessage-deflate and relies on that limit; the demonstrated consequence is availability loss through excess allocation and processing.

The record

CVE
CVE-2026-77528
Published
Sep 18, 2026
Updated
Sep 18, 2026
Vendor
Crossbar.io
Product
Autobahn|Python
Classifications
CWE-770, CWE-409, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 18, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 26.7.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Crossbar.io · Autobahn|Pythonversion=< 26.7.1

Published CVSS scores

5.3GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
CWE-409Improper Handling of Highly Compressed Data (Data Amplification)
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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