How severe is CVE-2026-13221?

CVE-2026-13221 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability high.

Is CVE-2026-13221 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (36th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-13221?

CVE-2026-13221 affects Perl. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-13221?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2026-13221 published?

CVE-2026-13221 was published on 2026-07-13 and last updated on 2026-07-14.

CVE-2026-13221

CVE-2026-13221 is a critical-severity vulnerability in Perl with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-190.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
EPSS exploit prediction: 0% (36th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-190
Affected product: Perl
Published: 2026-07-13
Last modified: 2026-07-14

Description

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.

Frequently asked questions

What is CVE-2026-13221?: 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.
How severe is CVE-2026-13221?: CVE-2026-13221 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability high.
Is CVE-2026-13221 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (36th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-13221?: CVE-2026-13221 affects Perl. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-13221?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2026-13221 published?: CVE-2026-13221 was published on 2026-07-13 and last updated on 2026-07-14.

References

Affected products (1)

cpe:2.3:a:perl:perl:*:*:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

185.74.59.5 (ipv4-addr)
43.134.103.74 (ipv4-addr)
92.68.96.50 (ipv4-addr)
36.64.56.43 (ipv4-addr)