CVE-2026-86805

Summary

A time-of-check to time-of-use (TOCTOU) race condition in the dynamic loader (ld.so) of the GNU C Library (glibc) versions 2.14 through 2.44 allows a local attacker to escalate privileges. When expanding $ORIGIN in DT_RPATH for setuid/setgid (AT_SECURE) programs, glibc validates the lexically normalized search path against the trusted directories but then opens the raw, un-normalized path. On systems where the Linux fs.protected_hardlinks sysctl is disabled, a local attacker who hard-links such a program into an attacker-controlled directory and wins a race to replace an intermediate path component with a symbolic link can direct the loader outside the trusted directory, causing it to load an attacker-controlled shared object and execute arbitrary code with the elevated privileges of the program.

Exploitation requires an installed setuid or setgid binary whose DT_RPATH uses $ORIGIN followed by ".." traversal that normalizes into a trusted directory, and the ability to hard-link that binary and win the race by swapping a path component for a symbolic link. Major Linux-based OS distributions ship with fs.protected_hardlinks enabled by default and mitigate the vulnerability.

Affected Software

Weaknesses

• CWE-367: CWE-367 Time-of-check time-of-use (TOCTOU) race condition

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: no
  • Technical Impact: total

References

• https://sourceware.org/bugzilla/show_bug.cgi?id=34360
• https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=advisories/GLIBC-SA-2026-0022

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