In the Linux kernel, the following vulnerability has been resolved: gcov: use atomic counter updates to fix concurrent access crashes GCC's GCOV instrumentation can merge global branch counters with loop induction variables as an optimization. In inflate_fast(), the inner copy loops get transformed so that the GCOV counter value is loaded multiple times to compute the loop base address, start index, and end bound. Since GCOV counters are global (not per-CPU), concurrent execution on different CPUs causes the counter to change between loads, producing inconsistent values and out-of-bounds memory writes. The crash manifests during IPComp (IP Payload Compression) processing when inflate_fast() runs concurrently on multiple CPUs: BUG: unable to handle page fault for address: ffffd0a3c0902ffa RIP: inflate_fast+1431 Call Trace: zlib_inflate __deflate_decompress crypto_comp_decompress ipcomp_decompress [xfrm_ipcomp] ipcomp_input [xfrm_ipcomp] xfrm_input At the crash point, the compiler generated three loads from the same global GCOV counter (__gcov0.inflate_fast+216) to compute base, start, and end for an indexed loop. Another CPU modified the counter between loads, making the values inconsistent - the write went 3.4 MB past a 65 KB buffer. Add -fprofile-update=prefer-atomic to CFLAGS_GCOV at the global level in the top-level Makefile, guarded by a try-run compile test. The test compiles a minimal program with and without -fprofile-update=prefer-atomic using the full KBUILD_CFLAGS, then compares undefined symbols in the resulting object files. If prefer-atomic introduces new undefined references (such as __atomic_fetch_add_8 on i386 or __aarch64_ldadd8_relax on arm64 with outline-atomics), the flag is not added -- the kernel does not link against libatomic. On architectures where GCC inlines 64-bit atomic counter updates (x86_64, s390, ...) the test passes and the flag is enabled, preventing the compiler from merging counters with loop induction variables and fixing the observed concurrent-access crash. On architectures where the flag would introduce libatomic dependencies, it is silently omitted and behaviour is no worse than before this patch. Move the CFLAGS_GCOV block from its original position (before the arch Makefile include) to after the core KBUILD_CFLAGS assignments but before the scripts/Makefile.gcc-plugins include. This placement ensures the try-run test sees arch-specific flags (-m32, -march=, -mno-outline-atomics) while avoiding GCC plugin flags (-fplugin=) that would break the test on clean builds when plugin shared objects do not yet exist.

The Unity Linux 20 host has a package installed that is affected by a vulnerability as referenced in the UTSA-2026-098894 advisory.

    In the Linux kernel, the following vulnerability has been resolved:

    gcov: use atomic counter updates to fix concurrent access crashes

    GCC's GCOV instrumentation can merge global branch counters with loop     induction variables as an optimization.  In inflate_fast(), the inner copy     loops get transformed so that the GCOV counter value is loaded multiple     times to compute the loop base address, start index, and end bound.  Since     GCOV counters are global (not per-CPU), concurrent execution on different     CPUs causes the counter to change between loads, producing inconsistent     values and out-of-bounds memory writes.

    The crash manifests during IPComp (IP Payload Compression) processing when     inflate_fast() runs concurrently on multiple CPUs:

      BUG: unable to handle page fault for address: ffffd0a3c0902ffa       RIP: inflate_fast+1431       Call Trace:
       zlib_inflate
       __deflate_decompress        crypto_comp_decompress        ipcomp_decompress [xfrm_ipcomp]        ipcomp_input [xfrm_ipcomp]        xfrm_input

    At the crash point, the compiler generated three loads from the same     global GCOV counter (__gcov0.inflate_fast+216) to compute base, start, and     end for an indexed loop.  Another CPU modified the counter between loads,     making the values inconsistent - the write went 3.4 MB past a 65 KB     buffer.

    Add -fprofile-update=prefer-atomic to CFLAGS_GCOV at the global level in     the top-level Makefile, guarded by a try-run compile test.  The test     compiles a minimal program with and without -fprofile-update=prefer-atomic     using the full KBUILD_CFLAGS, then compares undefined symbols in the     resulting object files.  If prefer-atomic introduces new undefined     references (such as __atomic_fetch_add_8 on i386 or __aarch64_ldadd8_relax     on arm64 with outline-atomics), the flag is not added -- the kernel does     not link against libatomic.

    On architectures where GCC inlines 64-bit atomic counter updates (x86_64,     s390, ...) the test passes and the flag is enabled, preventing the     compiler from merging counters with loop induction variables and fixing     the observed concurrent-access crash.

    On architectures where the flag would introduce libatomic dependencies, it     is silently omitted and behaviour is no worse than before this patch.

    Move the CFLAGS_GCOV block from its original position (before the arch     Makefile include) to after the core KBUILD_CFLAGS assignments but before     the scripts/Makefile.gcc-plugins include.  This placement ensures the     try-run test sees arch-specific flags (-m32, -march=,
    -mno-outline-atomics) while avoiding GCC plugin flags (-fplugin=) that     would break the test on clean builds when plugin shared objects do not yet     exist.

Tenable has extracted the preceding description block directly from the Unity Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - gcov: use atomic counter updates to fix concurrent access crashes GCC's GCOV instrumentation can merge     global branch counters with loop induction variables as an optimization. In inflate_fast(), the inner copy     loops get transformed so that the GCOV counter value is loaded multiple times to compute the loop base     address, start index, and end bound. Since GCOV counters are global (not per-CPU), concurrent execution on     different CPUs causes the counter to change between loads, producing inconsistent values and out-of-bounds     memory writes. The crash manifests during IPComp (IP Payload Compression) processing when inflate_fast()     runs concurrently on multiple CPUs: BUG: unable to handle page fault for address: ffffd0a3c0902ffa RIP:
    inflate_fast+1431 Call Trace: zlib_inflate __deflate_decompress crypto_comp_decompress ipcomp_decompress     [xfrm_ipcomp] ipcomp_input [xfrm_ipcomp] xfrm_input At the crash point, the compiler generated three loads     from the same global GCOV counter (__gcov0.inflate_fast+216) to compute base, start, and end for an     indexed loop. Another CPU modified the counter between loads, making the values inconsistent - the write     went 3.4 MB past a 65 KB buffer. Add -fprofile-update=prefer-atomic to CFLAGS_GCOV at the global level in     the top-level Makefile, guarded by a try-run compile test. The test compiles a minimal program with and     without -fprofile-update=prefer-atomic using the full KBUILD_CFLAGS, then compares undefined symbols in     the resulting object files. If prefer-atomic introduces new undefined references (such as
    __atomic_fetch_add_8 on i386 or __aarch64_ldadd8_relax on arm64 with outline-atomics), the flag is not     added -- the kernel does not link against libatomic. On architectures where GCC inlines 64-bit atomic     counter updates (x86_64, s390, ...) the test passes and the flag is enabled, preventing the compiler from     merging counters with loop induction variables and fixing the observed concurrent-access crash. On     architectures where the flag would introduce libatomic dependencies, it is silently omitted and behaviour     is no worse than before this patch. Move the CFLAGS_GCOV block from its original position (before the arch     Makefile include) to after the core KBUILD_CFLAGS assignments but before the scripts/Makefile.gcc-plugins     include. This placement ensures the try-run test sees arch-specific flags (-m32, -march=, -mno-outline-     atomics) while avoiding GCC plugin flags (-fplugin=) that would break the test on clean builds when plugin     shared objects do not yet exist. (CVE-2026-63825)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
340518	Unity Linux 20.1050a Security Update: kernel (UTSA-2026-098894)	Nessus	Unity Linux Local Security Checks	Local	critical
327843	Linux Distros Unpatched Vulnerability : CVE-2026-63825	Nessus	Misc.	Local	critical

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