CVE-2018-20164

Severity: medium (CVSS 5.3 v3.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 3.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2019-02-13 · updated 2026-06-17
Weakness: CWE-185

Description

An issue was discovered in regex.yaml (aka regexes.yaml) in UA-Parser UAP-Core before 0.6.0. A Regular Expression Denial of Service (ReDoS) issue allows remote attackers to overload a server by setting the User-Agent header in an HTTP(S) request to a value containing a long digit string. (The UAP-Core project contains the vulnerability, propagating to all implementations.)

Affected products

Uaparser User Agent Parser-Core: before 0.6.0 — fixed in 0.6.0

How to fix

Upgrade to a fixed version: Uaparser User Agent Parser-Core 0.6.0. Check the vendor advisory for mitigations.

References

https://github.com/ua-parser/uap-core/commit/010ccdc7303546cd22b9da687c29f4a996990014
https://github.com/ua-parser/uap-core/commit/156f7e12b215bddbaf3df4514c399d683e6cdadc
https://github.com/ua-parser/uap-core/issues/332
https://www.x41-dsec.de/lab/advisories/x41-2018-009-uaparser/
https://github.com/ua-parser/uap-core/commit/010ccdc7303546cd22b9da687c29f4a996990014
https://github.com/ua-parser/uap-core/commit/156f7e12b215bddbaf3df4514c399d683e6cdadc
https://github.com/ua-parser/uap-core/issues/332
https://www.x41-dsec.de/lab/advisories/x41-2018-009-uaparser/

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