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CVE-2021-21317

Denial of Service in uap-core

5.3 MediumFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
Low

Exploit likelihood

2.52%Up 1.1 points since Apr 14, 2021
90%50%10%1%

What each source reports

CVE List Score used 5.3

Denial of Service in uap-core

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.

Record
CVE-2021-21317
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Weakness
CWE-400
Updated
2026-11-02
EUVDEUVD-2021-0561 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 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.

Record
EUVD-2021-0561
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Updated
2026-11-03
GitHub AdvisoriesGHSA-p4pj-mg4r-x6v4 7.5

Denial of Service in uap-core

Impact

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.

Patches

Please update uap-core to >= v0.11.0

Downstream packages such as uap-python, uap-ruby etc which depend upon uap-core follow different version schemes.

Record
GHSA-p4pj-mg4r-x6v4
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400, CWE-1333
Updated
2026-11-02
NVD 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 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.

Record
CVE-2021-21317
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:N/I:N/A:P
Weakness
CWE-400, CWE-1333
Updated
2026-11-02
OSV 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 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.

Record
CVE-2021-21317
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Updated
2026-11-02
OSVGHSA-p4pj-mg4r-x6v4 7.5

Denial of Service in uap-core

Impact

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.

Patches

Please update uap-core to >= v0.11.0

Downstream packages such as uap-python, uap-ruby etc which depend upon uap-core follow different version schemes.

Record
GHSA-p4pj-mg4r-x6v4
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-1333, CWE-400
Updated
2026-11-02
OSVUBUNTU-CVE-2021-21317 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 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.

Record
UBUNTU-CVE-2021-21317
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
uap-core
npm
 before 0.11.0
0.11.0
uap-core
Ubuntu:20.04:LTS
 All versions, plus listed versions
20190213-2
 None known
uap-core
Ubuntu:22.04:LTS
 All versions, plus listed versions
1:0.12.0-11:0.13.0-11:0.14.0-11:0.15.0-1
 None known
uap-core
Ubuntu:24.04:LTS
 All versions, plus listed versions
1:0.18.0-1
 None known
uap-core
Ubuntu:25.10
 All versions, plus listed versions
1:0.18.0-1
 None known
uap-core
Ubuntu:26.10
 All versions, plus listed versions
1:0.18.0-1build1
 None known
uap-core
Ubuntu:26.04:LTS
 All versions, plus listed versions
1:0.18.0-11:0.18.0-1build1
 None known

History

History
RecordedChangedSources
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-21317 is a medium vulnerability (CVSS 5.3) in Ua-parser Uap-core, published February 2, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 2.52%, the 84th percentile. Fixed in uap-core 0.11.0.

References

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