The vulnerability in glibc's EUC_JISX0213 to UCS-4 conversion arises from improper handling of sequences that decode into two code points. When the output buffer can only hold the first code point, the second is stored as a pending character and the converter returns E2BIG. However, the pending character is never cleared after being emitted on the next call, causing the converter to repeatedly emit the same character without consuming further input. This results in an infinite loop, causing the calling application to hang. The issue affects glibc versions from 2.3 up to and including 2.44. The input must be attacker-controlled and the output buffer must be small enough to trigger the condition. This vulnerability is tracked as CWE-835 (Loop with unreachable exit condition). A related issue in SHIFT_JISX0213 is tracked separately as CVE-2026-77117.

The vulnerability causes a denial of service condition by hanging the affected application during character set conversion. There is no impact on confidentiality or integrity. The attack requires attacker-controlled input and specific buffer conditions. The affected character set (EUC_JISX0213) is uncommon, limiting the exposure. No known exploits are reported in the wild.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, applications should avoid converting attacker-controlled EUC_JISX0213 input with small output buffers. Monitoring vendor communications for updates is recommended.