CVE-2026-13221 Details
Perl versions through 5.43.9 produce silently incorrect regular expression matches when an alternation of more than 65535 fixed string branches is compiled into a trie in Perl_study_chunk.

When such branches are combined into a trie, the delta between the first branch and the shared tail is stored in a 16-bit field. A branch count above 65535 overflows the field, and the trie's match decision table is truncated with no warning or error.

A pattern of this shape produces false positive matches (matching strings it should not) and false negative matches (failing to match strings it should). When such a pattern gates an access or filtering decision, the result is wrong.
View at NVD
Exploit prediction scoring system (EPSS) score for CVE-2026-13221
EPSS (Exploit Prediction Scoring System): EPSS predicts the likelihood that a vulnerability will be exploited in the wild. A higher percentage means a greater chance of an exploit occurring. The EPSS model produces a probability score between 0 and 1 (0 and 100%).
0.43 Probability of exploitation activity being observed over the next 30 days (35th percentile)
CVSS score for CVE-2026-13221
CVSS (Common Vulnerability Scoring System): An open framework owned and managed by FIRST.Org, Inc. that assigns a numerical score from 0 to 10 to software vulnerabilities to indicate their severity.
9.1 Critical
Products affected by CVE-2026-13221
Perl 5.10.0
Perl 5.10.1
Perl 5.12.1
Perl 5.12.2
Perl 5.12.3
DVE Score by Bitsight AI
DVE scores complement traditional static scoring systems like CVSS with Bitsight AI powered real-time threat intelligence and underground cyber criminal activity so that security teams can reduce alert fatigue and focus on vulnerabilities most likely to be exploited.
Low
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CVE-2026-13221 Global Footprint

Top 10 Identified Countries

Country Observations Percentage
US 21,388 35.38%
DE 5,615 9.29%
GB 4,997 8.27%
JP 4,343 7.18%
FR 2,963 4.90%
CN 2,326 3.85%
RU 1,712 2.83%
CA 1,562 2.58%
CZ 1,119 1.85%
ID 851 1.41%

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CVE-2026-13221 Industry Footprint

Top 10 Identified Industries

*Service provider organizations (typically Technology and Telecommunications) are disproportionally represented in the results given their upstream ownership of end-user infrastructure. See our FAQs.

Industry* Observations Percentage
Technology 26,222 63.41%
Telecommunications 10,964 26.51%
Education 2,738 6.62%
Government/Politics 378 0.91%
Utilities 261 0.63%
Business Services 199 0.48%
Food Production 185 0.45%
Legal 67 0.16%
Media/Entertainment 45 0.11%
Energy/Resources 44 0.11%

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