CVE-2026-13221

CRITICALNVD 9.19.1
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to NVD's CVSS score.

Score 9.1 from GitHub Security Advisory (severity: CRITICAL) published 2026-07-13. NVD baseline CVSS 9.1; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, NVD CVSS v3
Trending — Patch released this week
9.1EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.4%CVSS: 9.1Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Fixed versions, as the CVE record's CNA (CPAN Security Group) states them: "Upgrade to Perl 5.40.5, 5.42.3 or 5.44.0 or later, or apply the upstream patch."

Perl versions before 5.40.5-RC1, from 5.41.0 before 5.42.3-RC1, from 5.43.0 before 5.43.10 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.

CVSS v3
9.1
EG Score
9.1CRITICALmedium confidence
EG Risk
56
EG Risk 56/100

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed (value × EchelonGraph’s weight)
Severity91% × 45%
The EG Score, 9.1 of 10.
Exploitation0.4% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability100% × 15%
CISA's SSVC Automatable value: yes (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Attend at high (mission-essential systems).
Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.4%
EPSS %ILE
35th
KEV
Not listed

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; 60 days if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

July 13, 2026

Last Modified

September 8, 2026

Advisory Details (3)

Auto-updated Sep 15, 2026
Patch available.
Web page

oss-security - 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

http://www.openwall.com/lists/oss-security/2026/07/13/5
Web page

Regexp memory corruption with large tries · Issue #23388 · Perl/perl5 · GitHub

https://github.com/Perl/perl5/issues/23388

Patch Availability(11)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
ubuntuperl-modules-5.40 (5.40.1-7ubuntu0.3) @ resolute2026-10-14ubuntu
ubuntuperl-modules-5.22 (5.22.1-9ubuntu0.9+esm3) @ xenial2026-10-14ubuntu
ubuntuperl-modules-5.38 (5.38.2-3.2ubuntu0.4) @ noble2026-10-14ubuntu
redhatcostmanagement/costmanagement-ui-rhel10:17914608512026-10-08redhat
redhatopenshift/ose-rhel-coreos-9:4.22.9.8.202609221802-02026-09-29redhat
redhatrhui5/rhua-rhel9:17894780952026-09-16redhat
redhatperl:5.32-8100020260826134600.651ee29f2026-09-14redhat
redhatperl-4:5.26.3-423.el8_10.12026-09-14redhat
redhatperl-4:5.32.1-484.el9_82026-09-14redhat
redhatperl-4:5.40.2-515.el10_22026-09-14redhat
redhatperl-main-5.42.2-524.3.hum12026-07-15redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(5 across 5 ecosystems)
Alpine:v3.24(1)
PackageVulnerable rangeFix by version rangeDependents
perl—
  • every version up to 5.42.2-r1: fixed in 5.42.2-r1
—
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
perl5.32.1-4 ... 5.44.0-1 (59 versions)
  • every version on: no fix on record
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
perl5.36.0-7, 5.36.0-7+deb12u1, 5.36.0-7+deb12u2, 5.36.0-7+deb12u3
  • every version up to 5.36.0-7+deb12u4: fixed in 5.36.0-7+deb12u4
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
perl5.40.1-6
  • every version up to 5.40.1-6+deb13u1: fixed in 5.40.1-6+deb13u1
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
perl5.40.1-6 ... 5.42.2-3 (9 versions)
  • every version up to 5.42.3-1: fixed in 5.42.3-1
—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Additional Vendor Advisories

(7)

Data Freshness Timeline

(refreshed 18× in last 7d / 52× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 100 of 579 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 479 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-14 12:33 UTCEG score recompute
  2. 2026-10-14 12:33 UTCVendor advisory
  3. 2026-10-14 12:33 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  4. 2026-10-13 16:33 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  5. 2026-10-13 11:09 UTCVendor advisory
  6. 2026-10-13 11:09 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  7. 2026-10-12 16:35 UTCEG score recompute
  8. 2026-10-12 16:33 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  9. 2026-10-12 09:47 UTCVendor advisory
  10. 2026-10-12 09:47 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  11. 2026-10-11 20:11 UTCEG score recompute
  12. 2026-10-11 18:24 UTCEG score recompute
  13. 2026-10-11 14:57 UTCEG score recompute
  14. 2026-10-11 13:48 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  15. 2026-10-10 19:59 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  16. 2026-10-09 20:06 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  17. 2026-10-08 17:11 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  18. 2026-10-07 23:47 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  19. 2026-10-06 15:17 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  20. 2026-10-05 17:42 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  21. 2026-10-04 23:21 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  22. 2026-10-03 14:25 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  23. 2026-10-01 19:49 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  24. 2026-10-01 14:13 UTCEG score recompute
  25. 2026-10-01 14:13 UTCVendor advisory
Show 75 more
  1. 2026-10-01 14:13 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  2. 2026-09-30 15:02 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  3. 2026-09-29 15:20 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  4. 2026-09-28 13:50 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  5. 2026-09-28 13:17 UTCVendor advisory
  6. 2026-09-28 13:17 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  7. 2026-09-28 09:31 UTCEG score recompute
  8. 2026-09-28 09:31 UTCVendor advisory
  9. 2026-09-28 09:31 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  10. 2026-09-26 15:58 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  11. 2026-09-24 10:05 UTCEG score recompute
  12. 2026-09-24 10:05 UTCVendor advisory
  13. 2026-09-24 10:05 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  14. 2026-09-23 13:47 UTCEPSS rescoreEPSS 0.4% · 37th percentile
  15. 2026-09-23 09:12 UTCVendor advisory
  16. 2026-09-23 09:12 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  17. 2026-09-23 05:25 UTCEG score recompute
  18. 2026-09-23 05:25 UTCVendor advisory
  19. 2026-09-23 05:25 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  20. 2026-09-20 20:15 UTCEPSS rescoreEPSS 0.4% · 37th percentile
  21. 2026-09-18 19:27 UTCEPSS rescoreEPSS 0.4% · 37th percentile
  22. 2026-09-18 10:06 UTCVendor advisory
  23. 2026-09-18 10:06 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  24. 2026-09-18 05:02 UTCEG score recompute
  25. 2026-09-18 05:02 UTCVendor advisory
  26. 2026-09-18 05:02 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  27. 2026-09-16 05:14 UTCEPSS rescoreEPSS 0.4% · 36th percentile
  28. 2026-09-14 11:07 UTCVendor advisory
  29. 2026-09-14 11:07 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  30. 2026-09-14 06:51 UTCVendor advisory
  31. 2026-09-14 06:51 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  32. 2026-09-14 03:11 UTCVendor advisory
  33. 2026-09-14 03:11 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  34. 2026-09-13 23:32 UTCEG score recompute
  35. 2026-09-13 23:32 UTCVendor advisory
  36. 2026-09-13 23:32 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  37. 2026-09-13 16:46 UTCEPSS rescoreEPSS 0.4% · 36th percentile
  38. 2026-09-13 16:30 UTCVendor advisory
  39. 2026-09-13 16:30 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  40. 2026-09-13 11:51 UTCVendor advisory
  41. 2026-09-13 11:51 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  42. 2026-09-13 08:00 UTCVendor advisory
  43. 2026-09-13 08:00 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  44. 2026-09-12 17:09 UTCEG score recompute
  45. 2026-09-12 17:09 UTCVendor advisory
  46. 2026-09-12 17:09 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  47. 2026-09-12 15:00 UTCEPSS rescoreEPSS 0.4% · 36th percentile
  48. 2026-09-12 13:27 UTCVendor advisory
  49. 2026-09-12 13:27 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  50. 2026-09-12 07:32 UTCVendor advisory
  51. 2026-09-12 07:32 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  52. 2026-09-12 01:51 UTCEG score recompute
  53. 2026-09-12 01:51 UTCVendor advisory
  54. 2026-09-12 01:51 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  55. 2026-09-11 14:52 UTCEPSS rescoreEPSS 0.4% · 36th percentile
  56. 2026-09-11 09:36 UTCEPSS rescoreEPSS 0.4% · 36th percentile
  57. 2026-09-10 09:34 UTCEPSS rescoreEPSS 0.4% · 36th percentile
  58. 2026-09-08 22:52 UTCEG score recompute
  59. 2026-09-08 22:52 UTCVendor advisory
  60. 2026-09-08 22:52 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  61. 2026-09-08 22:00 UTCEPSS rescoreEPSS 0.4% · 36th percentile
  62. 2026-09-08 01:57 UTCEG score recompute
  63. 2026-09-08 01:57 UTCVendor advisory
  64. 2026-09-08 01:57 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  65. 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.4% · 36th percentile
  66. 2026-09-06 13:50 UTCEG score recompute
  67. 2026-09-06 13:50 UTCVendor advisory
  68. 2026-09-06 13:50 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  69. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.4% · 36th percentile
  70. 2026-09-06 05:23 UTCVendor advisory
  71. 2026-09-06 05:23 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  72. 2026-09-06 01:36 UTCVendor advisory
  73. 2026-09-06 01:36 UTCGHSA enrichmentGHSA-whhx-pv66-xhgq · GitHub severity CRITICAL · GitHub CVSS 9.1
  74. 2026-09-05 21:25 UTCEG score recompute
  75. 2026-09-05 21:25 UTCVendor advisory

Frequently asked(5)

What is CVE-2026-13221?
CVE-2026-13221 is a critical-severity vulnerability; its CVE record was published on July 13, 2026. Perl versions before 5.40.5-RC1, from 5.41.0 before 5.42.3-RC1, from 5.43.0 before 5.43.10 produce silently incorrect regular expression matches when an alternation of more than 65535 fixed string branches is compiled into a trie in Perlstudychunk. When such branches are combined into a trie, the…
When was the CVE record for CVE-2026-13221 published?
The CVE record for CVE-2026-13221 was published on July 13, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of September 8, 2026; the record at its source may have been updated since.
Is CVE-2026-13221 actively exploited?
CVE-2026-13221 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.4% probability of exploitation in the next 30 days (35th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-13221?
CVE-2026-13221 has a CVSS v3 base score of 9.1 (NVD).
How do I remediate CVE-2026-13221?
A fix for CVE-2026-13221 is available: update to the fixed version the vendor names in its advisory. Fixed versions, as the CVE record's CNA (CPAN Security Group) states them: "Upgrade to Perl 5.40.5, 5.42.3 or 5.44.0 or later, or apply the upstream patch." The vendor advisories EchelonGraph has for CVE-2026-13221 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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