Bug 2538209 (CVE-2026-86805)

Summary: CVE-2026-86805 glibc: glibc: Privilege escalation and arbitrary code execution via TOCTOU race condition in dynamic loader
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, ashankar, codonell, dj, dpaolell, fweimer, jdelft, jupierce, lgarciaa, mbiarnes, pfrankli, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in glibc, specifically within its dynamic loader (ld.so). A local attacker can exploit a time-of-check to time-of-use (TOCTOU) race condition to escalate privileges and execute arbitrary code. This occurs when the dynamic loader expands $ORIGIN in DT_RPATH for setuid/setgid programs, validating a normalized path but then opening an un-normalized path. By hard-linking such a program and winning a race to swap a path component with a symbolic link, an attacker can direct the loader to an attacker-controlled shared object, gaining elevated privileges. This vulnerability is mitigated on systems with fs.protected_hardlinks enabled.
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Description OSIDB Bzimport 2026-09-22 17:25:55 UTC 
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.