CVE-2026-4177
Heap overflow in YAML::Syck emitter (Perl) <=1.36
Is CVE-2026-4177 being exploited?
Not confirmed. CVE-2026-4177 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.43% probability of exploitation in the next 30 days.
How severe is CVE-2026-4177?
CVE-2026-4177 is rated Critical with a CVSS score of 9.1. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-4177?
Yes. A fix has been recorded for CVE-2026-4177. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-4177 affect?
CVE-2026-4177 affects YAML::Syck (Perl) <= 1.36. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-4177?
Upgrade to YAML::Syck >=1.37
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Heap overflow and memory corruption via YAML emitter; attacker could crash or execute code in affected Perl apps.
Patch when possible
- affected<= 1.36
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.