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CVE-2020-7663 — Regular Expression Denial of Service in...

HIGH

Regular Expression Denial of Service in websocket-extensions (RubyGem)

Published June 5, 2020Updated July 8, 2026Source: osv

Summary

### Impact The ReDoS flaw allows an attacker to exhaust the server's capacity to process incoming requests by sending a WebSocket handshake request containing a header of the following form: Sec-WebSocket-Extensions: a; b="\c\c\c\c\c\c\c\c\c\c ... That is, a header containing an unclosed string parameter value whose content is a repeating two-byte sequence of a backslash and some other character. The parser takes exponential time to reject this header as invalid, and this will block the processing of any other work on the same thread. Thus if you are running a single-threaded server, such a request can render your service completely unavailable. ### Patches Users should upgrade to version 0.1.5. ### Workarounds There are no known work-arounds other than disabling any public-facing WebSocket functionality you are operating. ### References - https://blog.jcoglan.com/2020/06/02/redos-vulnerability-in-websocket-extensions/

Advisory Timeline

  • First published June 5, 2020 (2320 days ago).
  • Last revised July 8, 2026 — 2224 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

Bundler
Update websocket-extensions to 0.1.5 or later
gem install websocket-extensions -v 0.1.5

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (1)

Affects 1 ecosystem: rubygems (1).

PackageEcosystemAffectedFixed In
websocket-extensions
rubygems
0.1.0, 0.1.1, 0.1.2, 0.1.3 (+1 more)0.1.5

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

  • CWE-400
    Uncontrolled Resource ConsumptionMITRE

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 8.2 score means for each attack dimension.

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

References

Frequently Asked Questions

What is CVE-2020-7663?
Regular Expression Denial of Service in websocket-extensions (RubyGem) This vulnerability has been assigned a severity rating of HIGH (CVSS score: 8.2/10).
How do I check if my project is affected by CVE-2020-7663?
CVE-2020-7663 affects websocket-extensions. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2020-7663 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
8.2

High exploitability or significant impact. Prioritize remediation within days.

Also Known As

GHSA-g6wq-qcwm-j5g2
SNYK-RUBY-WEBSOCKETEXTENSIONS-570830

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