The vulnerability CVE-2026-3276 in CPython arises from the unicodedata.normalize() function's handling of Unicode input. Specifically, when the input contains long runs of combining characters with alternating Canonical Combining Class values, the function can take excessive CPU time to process. This behavior affects all normalization forms supported by the function. The issue is classified under CWE-407 (Improper Resource Management), indicating a potential denial-of-service condition due to resource exhaustion. The CVSS 4.0 base score is 6.3, reflecting a medium severity with network attack vector, low attack complexity, no privileges or user interaction required, and limited availability impact.

The vulnerability can lead to excessive CPU consumption when processing crafted Unicode input, potentially causing denial-of-service conditions by degrading performance or making the application unresponsive. There is no indication of data loss, privilege escalation, or confidentiality impact. No active exploitation has been reported.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since no official fix or remediation level is provided, users should monitor the Python Software Foundation advisories for updates. Until a fix is available, avoid processing untrusted or specially crafted Unicode input with unicodedata.normalize() in performance-critical or exposed environments.