# CVE-2026-115819: One-byte buffer overflow in wide scanf %s and %[ conversions

Status: published. Published: 2026-11-11. Updated: 2026-11-11.

Calling the wide scanf family of functions (swscanf, fwscanf, wscanf, vswscanf, vfwscanf and vwscanf) with a %s or %[ conversion without the 'l' length modifier in the GNU C Library version 2.2 to version 2.44 writes an extra null byte one past the end of the destination array when the converted multibyte string and its terminating null byte exactly fill that array.

These conversions store each wide input character into the caller's char array as a multibyte sequence.  The conversion ends with the sequence that returns to the initial shift state, which also stores the terminating null byte, and the functions then append a second null byte.  A destination sized for the converted string and one terminator, as the C standard requires the caller to provide, is therefore written one byte past its end.  The out-of-bounds byte is always a null byte, which may corrupt adjacent data or crash the process.  An attacker who supplies the input can trigger the overflow with a string whose converted length exactly fills the destination.

The narrow scanf functions, the %ls and %l[ conversions into a wchar_t array, and the 'a' and 'm' allocation modifiers are not affected, and storing a wide scanf conversion into a narrow char array is uncommon.  This issue affects all architectures and ABIs supported by the GNU C Library.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- The GNU C Library / glibc: ≥ 2.2; ≤ 2.44 (affected, custom). Source: CNA: glibc

## Severity and prioritization

- CVSS 3.1: 4.8 (medium); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L; source: CNA: glibc

- CVSS 3.1: 4.8 (medium); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L; source: NVD: 3ff69d7a-14f2-4f67-a097-88dee7810d18

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-193

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://sourceware.org/bugzilla/show_bug.cgi?id=34989 (CNA: glibc; issue-tracking)

- https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=advisories/GLIBC-SA-2026-0027 (CNA: glibc; vendor-advisory)

- https://sourceware.org/bugzilla/show_bug.cgi?id=34989 (3ff69d7a-14f2-4f67-a097-88dee7810d18)

- https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=advisories/GLIBC-SA-2026-0027 (3ff69d7a-14f2-4f67-a097-88dee7810d18)

## Provenance

- CNA: glibc: https://www.cve.org/CVERecord?id=CVE-2026-115819; retrieved 2026-11-11; source updated 2026-11-11

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-115819; retrieved 2026-11-11; source updated 2026-11-11

Revision: aa01de586d182e90ff9cf0b67764fa5f60fe334b9db16d3aea01a4c4f7bf4b1a

Canonical: https://y2.dev/cve/CVE-2026-115819

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