CVE-2026-66858: Apache Thrift, Apache Thrift, Apache Thrift, Apache Thrift, Apache Thrift, Apache Thrift: skip() does not apply the recursion limit (Python accelerator, PHP, Perl, Lua, Smalltalk, OCaml)

Is it exploited?

Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of 29 Oct 2026. If CISA adds it, this page shows it as known exploited.

How likely is exploitation in the next 30 days?

0.3%

EPSS score, percentile 23.4 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?

8.7 High

CVSS v4.0 base score, given by the CNA

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (2)

Which versions are affected?

Affected

• before 0.25.0
• before 0.25.0
• before 0.25.0
• before 0.25.0
• before 0.25.0
• before 0.25.0

Versions by product

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026; CVE List, as of 29 Oct 2026. About the data.

What to do

Advisories and patches

• lists.apache.org (Vendor advisory)
• lists.apache.org (Vendor advisory)

This summary is based on the CVE record as of 29 Oct 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

As listed in the CVE record.

Versions not listed are: unaffected.

Versions not listed are: unaffected.

Versions not listed are: unaffected.

Versions not listed are: unaffected.

Versions not listed are: unaffected.

Versions not listed are: unaffected.

Source: CVE List, as of 29 Oct 2026. About the data.

About this vulnerability

The protocol skip routine in several Apache Thrift bindings did not apply the binding's recursion limit, so a message that nests unknown fields deeply enough can exhaust the stack. Affected: the Python C++ accelerator (the pure-Python protocols are not affected), the PHP library and its thrift_protocol extension, and the Perl, Lua, Smalltalk and OCaml libraries. This issue affects Apache Thrif…

Summary: CVE record, as of 29 Oct 2026.

• CISA has not added CVE-2026-66858 to its Known Exploited Vulnerabilities (KEV) catalog, as of 29 Oct 2026.
• The CVE record was published on 2 Oct 2026.
• The CVE record carries a CVSS v4.0 base score of 8.7 (High), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 0.3% (percentile 23.4), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
• CISA's SSVC assessment in the CVE record: exploitation none, automatable yes, technical impact partial.
• The credits in the CVE record name Anthropic (Claude) as finder.

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; CVE List, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026. About the data.

Description

Apache Thrift, Apache Thrift, Apache Thrift, Apache Thrift, Apache Thrift, Apache Thrift: skip() does not apply the recursion limit (Python accelerator, PHP, Perl, Lua, Smalltalk, OCaml)

The protocol skip routine in several Apache Thrift bindings did not apply the binding's recursion limit, so a message that nests unknown fields deeply enough can exhaust the stack. Affected: the Python C++ accelerator (the pure-Python protocols are not affected), the PHP library and its thrift_protocol extension, and the Perl, Lua, Smalltalk and OCaml libraries. This issue affects Apache Thrift: before 0.25.0. Users are recommended to upgrade to version 0.25.0, which fixes the issue.

Source: CVE List, as of 29 Oct 2026. About the data.

Timeline

Known exploited Apache vulnerabilities

• CVE-2016-3081: Apache Struts Command Injection Vulnerability (added 8 Oct 2026)
• CVE-2026-34486: Apache Tomcat Missing Encryption of Sensitive Data Vulnerability (added 4 Aug 2026)
• CVE-2026-34197: Apache ActiveMQ Improper Input Validation Vulnerability (added 16 Apr 2026)
• CVE-2024-38475: Apache HTTP Server Improper Escaping of Output Vulnerability (added 1 May 2025)
• CVE-2025-24813: Apache Tomcat Path Equivalence Vulnerability (added 1 Apr 2025)