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Not in CISA KEV
HIGH severity

CVE-2020-5243 — uap-core

HIGHFix: ua-parser/uap-core@0afd61e

CVE-2020-5243 is a high-severity (CVSS 7.5) Improper Input Validation vulnerability in uap-core. 1 public exploit reference exists, so weaponization risk is real. A fix is available for uap-core — see the affected versions and patch details below.

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

Also known asGHSA-cmcx-xhr8-3w9p
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
1 known
Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
2.3%probability of exploitation in next 30 days
Lower Risk+0.03%
Lower risk than most CVEs83th percentile — riskier than 83% of all scored CVEsHighest risk
0.30%1.13%1.96%2.79%0.8%2.3%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2020-5243 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

1other npm packages depend on this — each one inherits the vulnerability until it's patched upstream
uap-corenpm
8Kdownloads / week

Description

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 &amp;gt;= 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

&amp;amp;quot;SmartWatch(&amp;amp;quot; + (&amp;amp;quot; &amp;amp;quot; * 3500) + &amp;amp;quot;z&amp;amp;quot;

e.g.

SmartWatch(                                   z

Regex 2:

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

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

&amp;amp;quot;;A Build HuaweiA&amp;amp;quot; + (&amp;amp;quot;4&amp;amp;quot; * 3500) + &amp;amp;quot;z&amp;amp;quot;

Regex 3:

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

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

&amp;amp;quot;HbbTV/0.0.0 (;LGE;&amp;amp;quot; + (&amp;amp;quot; &amp;amp;quot; * 3500) + &amp;amp;quot;z&amp;amp;quot;

Regex 4:

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

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

&amp;amp;quot;HbbTV/0.0.0 (;CUS:;&amp;amp;quot; + (&amp;amp;quot; &amp;amp;quot; * 3500) + &amp;amp;quot;z&amp;amp;quot;
&amp;amp;quot;HbbTV/0.0.0 (;&amp;amp;quot; + (&amp;amp;quot; &amp;amp;quot; * 3500) + &amp;amp;quot;z&amp;amp;quot;
&amp;amp;quot;HbbTV/0.0.0 (;z;&amp;amp;quot; + (&amp;amp;quot; &amp;amp;quot; * 3500) + &amp;amp;quot;z&amp;amp;quot;

Reported by Ben Caller @bcaller

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
📦npmuap-coreall versions0.7.3npm install uap-core@0.7.3
💎RubyGemsuser_agent_parserall versions2.6.0bundle update user_agent_parser --conservative

Affected Products

1 product · 1 configurations
Application
uap-coreuap-core_project
< 0.7.3
range
Exploits & PoCs
1

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

uap-core before 0.7.3 is vulnerable to a denial of service attack when p…

github.comNVDFeb 2020

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for uap-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update uap-core to 0.7.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-5243 is resolved across your whole dependency graph.

  3. Workarounds

    Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### 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 &amp;amp;gt;= 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
O3 Security · Impact-Aware SCA

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CVE-2020-5243: uap-core DoS — Fixed in 0.7.3