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CVE-2020-5243

Denial of Service in uap-core when processing crafted User-Agent strings

5.7 MediumFix available

CVE-2020-5243 is a medium vulnerability (CVSS 5.7) in Ua-parser Uap-core, published February 20, 2020. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 2.29%, the 83rd percentile. Fixed in uap-core 0.7.3.

uap-core before 0.7.3 is vulnerable to a denial of service attack when processing crafted User-Agent strings. 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 has been patched in uap-core 0.7.3.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
Low
User interaction
Required

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

2.29%Up 1.3 points since Apr 14, 2021
90%50%10%1%

What each source reports

CVE List Score used 5.7

Denial of Service in uap-core when processing crafted User-Agent strings

uap-core before 0.7.3 is vulnerable to a denial of service attack when processing crafted User-Agent strings. 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 has been patched in uap-core 0.7.3.

Record
CVE-2020-5243
CVSS 3.1
5.7 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
Weakness
CWE-20
Updated
2026-11-02
EUVDEUVD-2020-0301 5.7

uap-core before 0.7.3 is vulnerable to a denial of service attack when processing crafted User-Agent strings. 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 has been patched in uap-core 0.7.3.

Record
EUVD-2020-0301
CVSS 3.1
5.7 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
Updated
2026-11-03
GitHub AdvisoriesGHSA-cmcx-xhr8-3w9p 5.7

Denial of Service in uap-core when processing crafted User-Agent strings

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 >= v0.7.3

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

Details

Each vulnerable regular expression reported here contains 3 overlapping capture groups. Backtracking has approximately cubic time complexity with respect to the length of the user-agent string.

Regex 1:

\bSmartWatch *\( *([^;]+) *; *([^;]+) *;

is vulnerable in portion *([^;]+) * and can be attacked with

"SmartWatch(" + (" " * 3500) + "z"

e.g.

SmartWatch(                                   z

Regex 2:

; *([^;/]+) Build[/ ]Huawei(MT1-U06|[A-Z]+\d+[^\);]+)[^\);]*\)

is vulnerable in portion \d+[^\);]+[^\);]* and can be attacked with

";A Build HuaweiA" + ("4" * 3500) + "z"

Regex 3:

(HbbTV)/[0-9]+\.[0-9]+\.[0-9]+ \([^;]*; *(LG)E *; *([^;]*) *;[^;]*;[^;]*;\)

is vulnerable in portion *([^;]*) * and can be attacked with

"HbbTV/0.0.0 (;LGE;" + (" " * 3500) + "z"

Regex 4:

(HbbTV)/[0-9]+\.[0-9]+\.[0-9]+ \([^;]*; *(?:CUS:([^;]*)|([^;]+)) *; *([^;]*) *;.*;

is vulnerable in portions *(?:CUS:([^;]*)|([^;]+)) * and *([^;]*) * and can be attacked with

"HbbTV/0.0.0 (;CUS:;" + (" " * 3500) + "z"
"HbbTV/0.0.0 (;" + (" " * 3500) + "z"
"HbbTV/0.0.0 (;z;" + (" " * 3500) + "z"

Reported by Ben Caller @bcaller

Record
GHSA-cmcx-xhr8-3w9p
CVSS 3.1
5.7 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
Weakness
CWE-20, CWE-1333
Updated
2026-11-02
NVD 5.7

uap-core before 0.7.3 is vulnerable to a denial of service attack when processing crafted User-Agent strings. 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 has been patched in uap-core 0.7.3.

Record
CVE-2020-5243
CVSS 3.1
5.7 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:N/I:N/A:P
Weakness
CWE-20, CWE-1333
Updated
2026-11-02
OSV 7.5

uap-core before 0.7.3 is vulnerable to a denial of service attack when processing crafted User-Agent strings. 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 has been patched in uap-core 0.7.3.

Record
CVE-2020-5243
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVDEBIAN-CVE-2020-5243 7.5

uap-core before 0.7.3 is vulnerable to a denial of service attack when processing crafted User-Agent strings. 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 has been patched in uap-core 0.7.3.

Record
DEBIAN-CVE-2020-5243
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVGHSA-cmcx-xhr8-3w9p 5.7

Denial of Service in uap-core when processing crafted User-Agent strings

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 >= v0.7.3

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

Details

Each vulnerable regular expression reported here contains 3 overlapping capture groups. Backtracking has approximately cubic time complexity with respect to the length of the user-agent string.

Regex 1:

\bSmartWatch *\( *([^;]+) *; *([^;]+) *;

is vulnerable in portion *([^;]+) * and can be attacked with

"SmartWatch(" + (" " * 3500) + "z"

e.g.

SmartWatch(                                   z

Regex 2:

; *([^;/]+) Build[/ ]Huawei(MT1-U06|[A-Z]+\d+[^\);]+)[^\);]*\)

is vulnerable in portion \d+[^\);]+[^\);]* and can be attacked with

";A Build HuaweiA" + ("4" * 3500) + "z"

Regex 3:

(HbbTV)/[0-9]+\.[0-9]+\.[0-9]+ \([^;]*; *(LG)E *; *([^;]*) *;[^;]*;[^;]*;\)

is vulnerable in portion *([^;]*) * and can be attacked with

"HbbTV/0.0.0 (;LGE;" + (" " * 3500) + "z"

Regex 4:

(HbbTV)/[0-9]+\.[0-9]+\.[0-9]+ \([^;]*; *(?:CUS:([^;]*)|([^;]+)) *; *([^;]*) *;.*;

is vulnerable in portions *(?:CUS:([^;]*)|([^;]+)) * and *([^;]*) * and can be attacked with

"HbbTV/0.0.0 (;CUS:;" + (" " * 3500) + "z"
"HbbTV/0.0.0 (;" + (" " * 3500) + "z"
"HbbTV/0.0.0 (;z;" + (" " * 3500) + "z"

Reported by Ben Caller @bcaller

Record
GHSA-cmcx-xhr8-3w9p
CVSS 3.1
5.7 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
Weakness
CWE-1333, CWE-20
Updated
2026-11-02
OSVUBUNTU-CVE-2020-5243 5.7

uap-core before 0.7.3 is vulnerable to a denial of service attack when processing crafted User-Agent strings. 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 has been patched in uap-core 0.7.3.

Record
UBUNTU-CVE-2020-5243
CVSS 3.1
5.7 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
uap-core
npm
 before 0.7.3
0.7.3
user_agent_parser
RubyGems
 before 2.6.0
2.6.0
uap-core
Debian:12
 before 1:0.8.0-1
1:0.8.0-1
uap-core
Debian:13
 before 1:0.8.0-1
1:0.8.0-1
uap-core
Debian:14
 before 1:0.8.0-1
1:0.8.0-1
user_agent_parser
RubyGems
 before 2.6.0, plus listed versions
0.1.00.1.10.1.21.0.01.0.1
Show 18 moreShow less
1.0.22.0.02.1.02.1.12.1.22.1.32.1.42.1.52.2.02.3.02.3.12.3.22.4.02.4.12.5.02.5.12.5.22.5.3
2.6.0
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
WhenChangedSources
2026-11-03aliasesEUVD
2026-11-02createdCVE List, GitHub Advisories, NVD, OSV

References

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