GNU C Library security advisory batch discloses strfmon buffer overflow and DNS stub resolver abort

Two glibc advisories — GLIBC-SA-2026-0017 (buffer overflow in strfmon/strfmon_l, glibc 2.38–2.44) and GLIBC-SA-2026-0021 (DNS stub resolver assertion failure causing process aborts with ~200+ character search domains, glibc 2.26–2.44) — were published in the…

The GNU C Library published security advisories across its 2026-09-14 and 2026-09-17 update batches. GLIBC-SA-2026-0017 discloses a buffer overflow in strfmon and strfmon_l: calling these functions with right-justified width padding conversions can write past the end of the caller-supplied output buffer in glibc versions 2.38 through 2.44; exploitation requires an application code path that calls strfmon with attacker-influenced parameters. GLIBC-SA-2026-0021 discloses an assertion failure in the glibc DNS stub resolver: systems running glibc versions 2.26 through 2.44 abort when the search list in /etc/resolv.conf or the LOCALDOMAIN environment variable contains a domain of roughly 200 characters or more; the impact is a process abort (denial of service), not code execution. No CVE identifiers were provided in the reports.

• Advisory GLIBC-SA-2026-0017: buffer overflow in strfmon and strfmon_l right-justification padding
• GLIBC-SA-2026-0017 affects glibc versions 2.38 through 2.44
• GLIBC-SA-2026-0017 exploitation requires an app path calling strfmon with crafted conversion specs (attacker-influenced parameters)
• Advisory GLIBC-SA-2026-0021: assertion failure in the glibc DNS stub resolver
• GLIBC-SA-2026-0021 affects glibc versions 2.26 through 2.44
• GLIBC-SA-2026-0021 is triggered by search domains of roughly 200+ characters in /etc/resolv.conf or the LOCALDOMAIN environment variable
• GLIBC-SA-2026-0021 impact is process abort (denial of service), not code execution
• Advisories were published as part of the GNU C Library security update batches on 2026-09-14 and 2026-09-17