CVE-2020-7663Public exploitNetwork attack vector

Service interruption via ambiguous quoted-string regex backtracking

Published Jun 2, 2020 · Updated Aug 4, 2024

Regular expression denial of service in Faye websocket-extensions before 0.1.5 allows remote attackers to interrupt WebSocket servers. In lib/websocket/extensions/parser.rb, the QUOTED pattern lets backslash sequences match overlapping branches, causing exponential backtracking when a closing quote is absent. A crafted Sec-WebSocket-Extensions handshake reaches the flaw without authentication; on a single-threaded server, parsing blocks all other request work.

CVSS severity7.5
High
EPSS probability4.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Regular expression denial of service in Faye websocket-extensions before 0.1.5 allows remote attackers to interrupt WebSocket servers. In lib/websocket/extensions/parser.rb, the QUOTED pattern lets backslash sequences match overlapping branches, causing exponential backtracking when a closing quote is absent. A crafted Sec-WebSocket-Extensions handshake reaches the flaw without authentication; on a single-threaded server, parsing blocks all other request work.

The record

CVE
CVE-2020-7663
Published
Jun 2, 2020
Updated
Aug 4, 2024
Vendor
Faye
Product
websocket-extensions
Classifications
CWE-400, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 2, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record 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=All versions prior to 0.1.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Faye · websocket-extensionsversion=All versions prior to 0.1.5

Published CVSS scores

5.0NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1190Exploit Public-Facing Application

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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