CVE-2018-1000518: aaugustin websockets version 4 contains a CWE-409: Improper Handling of Highly Compressed Data (Data Amplifica

Q: How do I fix CVE-2018-1000518?

websockets: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2018-1000518 being exploited?

CVE-2018-1000518 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2018-1000518 affect?

CVE-2018-1000518 affects websockets. Severity is high (CVSS 7.5). aaugustin websockets version 4 contains a CWE-409: Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in Servers and clients, unless configured with compression=None that can result in Denial of Service by memory

Q: How urgent is CVE-2018-1000518?

Priority 56/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

HIGH 7.5REMOTEDOWNGRADE

CVE-2018-1000518 is a high-severity flaw (CVSS 7.5) affecting websockets. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

aaugustin websockets version 4 contains a CWE-409: Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in Servers and clients, unless configured with compression=None that can result in Denial of Service by memory exhaustion. This attack appear to be exploitable via Sending a specially crafted frame on an established connection. This vulnerability appears to have been fixed in 5.

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.8% (top 21%)
CISA exploited list	No
Weakness	CWE-400
Published	2018-06-26
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: websockets project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2018-06-26 16:29 UTCPublished CVE record published
2026-06-17 01:32 UTCUpdated Record last modified

websockets project websockets DOWNGRADE

Affected: 4.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.0

1. Check installed version

pip show websockets

2. No fixed release: DOWNGRADE to a release before 4.0

pip index versions websockets pip install "websockets<4.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2018-1000518?

websockets: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2018-1000518 being exploited?

CVE-2018-1000518 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2018-1000518 affect?

CVE-2018-1000518 affects websockets. Severity is high (CVSS 7.5). aaugustin websockets version 4 contains a CWE-409: Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in Servers and clients, unless configured with compression=None that can result in Denial of Service by memory

How urgent is CVE-2018-1000518?

Priority 56/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2021-33880 MEDIUM 5.9 UPGRADE DOWNGRADE The aaugustin websockets library before 9.1 for Python has an Observable Timing Discrepancy on servers when HT

References

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