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CVE-2026-5928 The GNU C Library CVE debrief

CVE-2026-5928 is a HIGH severity vulnerability in the GNU C Library version 2.43 or earlier. The ungetwc function may result in an attempt to read bytes before an allocated buffer, potentially leading to unintentional disclosure of neighboring data in the heap or a program crash. This vulnerability affects systems using the GNU C Library, particularly those with specific character encoding configurations. Users should review their exposure and apply patches or mitigations as needed.

Vendor
The GNU C Library
Product
glibc
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-04-20
Original CVE updated
2026-07-14
Advisory published
2026-04-20
Advisory updated
2026-07-14

Who should care

Users of GNU C Library version 2.43 or earlier should be aware of this vulnerability and take steps to mitigate it. This includes system administrators, developers using the GNU C Library in their applications, and security teams responsible for vulnerability management. Affected systems may be widespread, given the library's common use in many Linux distributions and other Unix-like operating systems.

Technical summary

The bug in the wide character pushback implementation (_IO_wdefault_pbackfail in libio/wgenops.c) causes ungetwc() to operate on the regular character buffer (fp->_IO_read_ptr) instead of the actual wide-stream read pointer (fp->_wide_data->_IO_read_ptr). This may result in an attempt to read bytes before an allocated buffer, potentially leading to data disclosure or a program crash. The vulnerability requires specific conditions, including overlapping single-byte and multi-byte character encodings.

Defensive priority

High priority should be given to patching or mitigating this vulnerability, as it has a CVSS score of 7.5 and is classified as HIGH severity. Given the potential for data disclosure or program crashes, swift action is necessary to protect sensitive systems and data.

Recommended defensive actions

  • Apply patches or updates to GNU C Library version 2.43 or earlier.
  • Use compensating controls to prevent exploitation.
  • Monitor for potential attacks or suspicious activity.
  • Perform inventory checks to identify affected systems.
  • Review and implement secure coding practices to minimize similar vulnerabilities.
  • Track exceptions and retest remediated assets to ensure effectiveness.

Evidence notes

The CVE record was published on 2026-04-20T21:16:36.963Z and was last modified on 2026-07-14T13:19:01.690Z. The NVD entry is currently Modified. Evidence is limited to public sources and may not reflect the full scope or impact of this vulnerability. Defenders should verify affected systems and review official advisories for specific guidance.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-04-20T21:16:36.963Z and has not been modified since then. The NVD entry is currently Modified.