CVE-2021-21317

Name: CVE-2021-21317
Creator: NVD / NIST
Published: 2021-02-16T18:15:12.583+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.3/10EPSS 2.52%

Last modified Jun 17, 2026

CVE-2021-21317 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. uap-core in an open-source npm package which contains the core of BrowserScope's original user agent string parser. In uap-core before version 0.11.0, some regexes are vulnerable to regular expression denial of service (REDoS) due to overlapping capture groups. EPSS estimates a 2.52% chance of exploitation in the next 30 days.

Description

uap-core in an open-source npm package which contains the core of BrowserScope's original user agent string parser. In uap-core before version 0.11.0, some regexes are vulnerable to regular expression denial of service (REDoS) due to overlapping capture groups. This allows remote attackers to overload a server by setting the User-Agent header in an HTTP(S) request to maliciously crafted long strings. This is fixed in version 0.11.0. Downstream packages such as uap-python, uap-ruby etc which depend upon uap-core follow different version schemes.

Metrics

CVSS 3.1

5.3/10

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

EPSS Probability

2.52%

82.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Uap-Core Project	Uap-Core	< 0.11.0

References

https://github.com/ua-parser/uap-core/commit/dc9925d458214cfe87b93e35346980612f6ae96cPatch
https://github.com/ua-parser/uap-core/security/advisories/GHSA-p4pj-mg4r-x6v4Third Party Advisory
https://www.npmjs.com/package/uap-coreProduct, Third Party Advisory
https://github.com/ua-parser/uap-core/commit/dc9925d458214cfe87b93e35346980612f6ae96cPatch
https://github.com/ua-parser/uap-core/security/advisories/GHSA-p4pj-mg4r-x6v4Third Party Advisory
https://www.npmjs.com/package/uap-coreProduct, Third Party Advisory

Timeline

Published: Feb 16, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-21317?

How severe is CVE-2021-21317?

CVE-2021-21317 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 2.52% probability of exploitation in the next 30 days.

How do I fix CVE-2021-21317?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-21317?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST