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GNU C Library security advisories: nscd stack overflow (GLIBC-SA-2026-0016) and strfmon buffer overflow (GLIBC-SA-2026-0017)

mediumVulnerabilityimportance 38
What's new: First merged summary of this story. The story began with GLIBC-SA-2026-0016 (nscd stack overflow, advisory dated 2026-09-10) and was extended on 2026-09-14 with a new advisory, GLIBC-SA-2026-0017, disclosing a buffer overflow in strfmon/strfmon_l affecting glibc 2.38 through 2.44. The reports do not conflict on any facts.
Merged summary · glm-5.3 · rewritten as coverage arrives

Two glibc advisories disclose a stack overflow in nscd triggered by oversized responses from a malicious DNS server, and a buffer overflow in strfmon/strfmon_l in glibc 2.38 through 2.44.

The GNU C Library issued two security advisories in September 2026. GLIBC-SA-2026-0016 (advisory update dated 2026-09-10, posted to oss-security by glibc maintainer Siddhesh Poyarekar) describes a stack overflow in the nscd service caused by unbounded alloca use; glibc 2.3.4 and newer can crash when a malicious DNS server returns oversized responses to DNS queries. Exploitation requires nscd to be enabled and the system to be using an untrusted DNS server, and the impact is degraded DNS resolution. GLIBC-SA-2026-0017 (published 2026-09-14) 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 2.38 through 2.44. Exploitation requires an application code path that calls strfmon with attacker-influenced parameters.

  • GLIBC-SA-2026-0016: stack overflow in nscd caused by unbounded alloca use
  • nscd crash affects glibc 2.3.4 and newer; triggered by a malicious DNS server returning oversized responses to DNS queries
  • Impact of the nscd issue is degraded DNS resolution; exploitation requires nscd enabled and the system using an untrusted DNS server
  • GLIBC-SA-2026-0016 advisory update dated 2026-09-10, posted to oss-security on 2026-09-11 by glibc maintainer Siddhesh Poyarekar
  • GLIBC-SA-2026-0017: buffer overflow in strfmon and strfmon_l with right-justified width padding conversions, writing past the end of the caller-supplied output buffer
  • strfmon/strfmon_l flaw affects glibc versions 2.38 through 2.44; exploitation requires an application code path calling strfmon with attacker-influenced parameters
  • GLIBC-SA-2026-0017 announced in the glibc security advisories update for 2026-09-14
VendorsGNU C Library
Productsglibcnscd
OrganizationsGNU Project

Coverage timeline

  1. · 5d ago
    oss-security· 28
    The GNU C Library security advisory update for 2026-09-10

    glibc advisory GLIBC-SA-2026-0016: nscd can crash from a stack overflow when an untrusted DNS server returns oversized responses.

  2. · 1d ago
    oss-security· 38
    The GNU C Library security advisories update for 2026-09-14

    glibc advisory GLIBC-SA-2026-0017 discloses a buffer overflow in strfmon/strfmon_l affecting versions 2.38 through 2.44.