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Fencer Intel
medium 5.7

CVE-2020-5243 json

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

published 6y ago modified 4mo ago also GHSA-cmcx-xhr8-3w9p , EUVD-2020-0301

cvss
5.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.3%
EPSS 2.3% chance of exploitation in 30 days, percentile 83%
public exploits
0
none known

Summary

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.

Patch / fix

  • npm uap-core 0.7.3
  • rubygems user_agent_parser 2.6.0
  • uap-core_project uap-core 0.7.3
  • uap-core Debian 14, Debian 13, Debian 12 1:0.8.0-1

debian advisories DEBIAN-CVE-2020-5243

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Exploit prediction

2.29% chance of exploitation in the next 30 days, higher than 83% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/ua-parser/uap-core/security/advisories/GHSA-cmcx-xhr8-3w9p referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.7 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P
GitHub 3.1 5.7 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
npm uap-core
<0.7.3
0.7.3
rubygems user_agent_parser
<2.6.0
2.6.0

Affected products

  • ua-parser uap-core

Classification

Weakness
  • CWE-20 Improper Input Validation
  • CWE-1333 Inefficient Regular Expression Complexity

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.