CVE-2021-21317: uap-core in an open-source npm package which contains the core of BrowserScope's original user agent string pa

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MEDIUM 5.3REMOTEUPGRADE

CVE-2021-21317 is a medium-severity flaw (CVSS 5.3) affecting uap-core. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 pa

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.5% (top 15%)
CISA exploited list	No
Weakness	CWE-400, CWE-1333
Published	2021-02-16
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: uap-core project

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

Am I affected?

Timeline

2021-02-16 18:15 UTCPublished CVE record published
2026-06-17 03:35 UTCUpdated Record last modified

uap-core project uap-core UPGRADE

Affected: < 0.11.0

Fixed in: 0.11.0

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls uap-core

2. UPGRADE to 0.11.0

npm install uap-core@">=0.11.0"

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-2021-21317?

uap-core: upgrade to 0.11.0. Exact commands for each OS are on this page.

Is CVE-2021-21317 being exploited?

CVE-2021-21317 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-2021-21317 affect?

CVE-2021-21317 affects uap-core. Severity is medium (CVSS 5.3). 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 overla

How urgent is CVE-2021-21317?

Priority 45/100. Remotely exploitable, no login, no user action

Software pages

npm packages vulnerabilities

Related CVEs

CVE-2020-5243 MEDIUM 5.7 UPGRADE uap-core before 0.7.3 is vulnerable to a denial of service attack when processing crafted User-Agent strings

References

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