What is CVE-2020-5243?

CVE-2020-5243 is a medium-severity improper input validation vulnerability in uap-core (npm), affecting versions < 0.7.3. It is fixed in 0.7.3, 2.6.0. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.

How severe is CVE-2020-5243?

CVE-2020-5243 has a CVSS score of 5.7 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.

Which packages are affected by CVE-2020-5243?

uap-core (npm) versions < 0.7.3; user_agent_parser (rubygems) versions < 2.6.0.

Is there a fix for CVE-2020-5243?

Yes. CVE-2020-5243 is fixed in 0.7.3, 2.6.0. Upgrade to this version or later.

Is CVE-2020-5243 exploitable, and should I be worried?

Whether CVE-2020-5243 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk.

What actually determines whether CVE-2020-5243 is exploitable, and how bad it is?

Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.

How do I fix CVE-2020-5243?

Upgrade: uap-core to 0.7.3 or later, user_agent_parser to 2.6.0 or later.

CVE-2020-5243 in uap-core

Q: How severe is CVE-2020-5243?

CVE-2020-5243 has a CVSS score of 5.7 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.

Q: Which packages are affected by CVE-2020-5243?

uap-core (npm) versions < 0.7.3; user_agent_parser (rubygems) versions < 2.6.0.

Q: Is there a fix for CVE-2020-5243?

Yes. CVE-2020-5243 is fixed in 0.7.3, 2.6.0. Upgrade to this version or later.

Q: Is CVE-2020-5243 exploitable, and should I be worried?

Whether CVE-2020-5243 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk.

Q: What actually determines whether CVE-2020-5243 is exploitable, and how bad it is?

Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.

Q: How do I fix CVE-2020-5243?

Upgrade: uap-core to 0.7.3 or later, user_agent_parser to 2.6.0 or later.

Summary

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

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

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.

The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.

CVE-2020-5243 has a CVSS score of 5.7 (Medium). The vector is network-reachable, low privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.7.3, 2.6.0); upgrading removes the vulnerable code path.

Affected versions

uap-core (< 0.7.3) user_agent_parser (< 2.6.0)

Security releases

uap-core → 0.7.3 (npm) user_agent_parser → 2.6.0 (rubygems)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

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Remediation advice

Please update uap-core to &gt;= v0.7.3

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

Frequently Asked Questions

What is CVE-2020-5243? CVE-2020-5243 is a medium-severity improper input validation vulnerability in uap-core (npm), affecting versions < 0.7.3. It is fixed in 0.7.3, 2.6.0. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
How severe is CVE-2020-5243? CVE-2020-5243 has a CVSS score of 5.7 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
Which packages are affected by CVE-2020-5243?
- uap-core (npm) (versions < 0.7.3)
- user_agent_parser (rubygems) (versions < 2.6.0)
Is there a fix for CVE-2020-5243? Yes. CVE-2020-5243 is fixed in 0.7.3, 2.6.0. Upgrade to this version or later.
Is CVE-2020-5243 exploitable, and should I be worried? Whether CVE-2020-5243 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
What actually determines whether CVE-2020-5243 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
How do I fix CVE-2020-5243?
- Upgrade uap-core to 0.7.3 or later
- Upgrade user_agent_parser to 2.6.0 or later

Other vulnerabilities in uap-core

CVE-IDSeverityPackage summary

CVE-2021-21317Highuap-core: Denial of Service in uap-core CVE-2018-20164Mediumuap-core: uap-core Regular Expression Denial of Service issue