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  • FreeBSD Security Advisory FreeBSD-SA-26:63.posixshm

    From FreeBSD Security Advisories@3:633/10 to All on Tuesday, August 25, 2026 21:00:08
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    ============================================================================= FreeBSD-SA-26:63.posixshm Security Advisory
    The FreeBSD Project

    Topic: TOCTOU race in POSIX shared memory large page configuration

    Category: core
    Module: posixshm
    Announced: 2026-08-25
    Credits: tsune of GMO Cybersecurity by Ierae, Inc.
    working with TrendAI Zero Day Initiative
    Affects: All supported versions of FreeBSD.
    Corrected: 2026-08-25 15:59:53 UTC (stable/15, 15.1-STABLE)
    2026-08-25 16:01:30 UTC (releng/15.1, 15.1-RELEASE-p3)
    2026-08-25 16:01:10 UTC (releng/15.0, 15.0-RELEASE-p13)
    2026-08-25 16:00:04 UTC (stable/14, 14.4-STABLE)
    2026-08-25 16:00:31 UTC (releng/14.4, 14.4-RELEASE-p9)
    CVE Name: CVE-2026-58094

    For general information regarding FreeBSD Security Advisories,
    including descriptions of the fields above, security branches, and the following sections, please visit <URL:https://security.FreeBSD.org/>.

    I. Background

    The POSIX shared memory object module supports "largepage" objects,
    which are shared memory objects backed by physically contiguous memory.
    Such objects can be accessed more efficiently in some cases. Largepage
    objects can be created using shm_create_largepage(3).

    II. Problem Description

    The FIOSSHMLPGCNF ioctl(2) operation configures the page size for a
    largepage shared memory object. This is intended to be used immediately
    after creating the object, before any memory is allocated for the object.
    The handler checked whether a page size had already been configured
    without holding the rangelock. Two concurrent callers could both
    observe an unconfigured object and set conflicting page sizes, leaving
    the object in an inconsistent state.

    III. Impact

    An unprivileged local user can exploit this race to escalate
    privileges.

    IV. Workaround

    No workaround is available.

    V. Solution

    Upgrade your vulnerable system to a supported FreeBSD stable or
    release / security branch (releng) dated after the correction date,
    and reboot the system.

    Perform one of the following:

    1) To update your vulnerable system installed from base system packages:

    Systems running a 15.0-RELEASE or later version of FreeBSD on the amd64 or arm64 platforms, which were installed using base system packages, can be updated via the pkg(8) utility:

    # pkg upgrade -r FreeBSD-base
    # shutdown -r +10min "Rebooting for a security update"

    2) To update your vulnerable system installed from binary distribution sets:

    Systems running a RELEASE version of FreeBSD on the amd64 or arm64 platforms which were not installed using base system packages can be updated via the freebsd-update(8) utility:

    # freebsd-update fetch
    # freebsd-update install
    # shutdown -r +10min "Rebooting for a security update"

    3) To update your vulnerable system via a source code patch:

    The following patches have been verified to apply to the applicable
    FreeBSD release branches.

    a) Download the relevant patch from the location below, and verify the
    detached PGP signature using your PGP utility.

    # fetch https://security.FreeBSD.org/patches/SA-26:63/posixshm.patch
    # fetch https://security.FreeBSD.org/patches/SA-26:63/posixshm.patch.asc
    # gpg --verify posixshm.patch.asc

    b) Apply the patch. Execute the following commands as root:

    # cd /usr/src
    # patch -E -p0 < /path/to/patch

    c) Recompile your kernel as described in <URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
    system.

    VI. Correction details

    This issue is corrected as of the corresponding Git commit hash in the following stable and release branches:

    Branch/path Hash Revision
    - ------------------------------------------------------------------------- stable/15/ 5990860ca841 stable/15-n285148 releng/15.1/ a372e73712cf releng/15.1-n283610 releng/15.0/ cec488c1669b releng/15.0-n281113 stable/14/ 6bfd894c8b14 stable/14-n275049 releng/14.4/ 840fd9dc7de2 releng/14.4-n273765
    - -------------------------------------------------------------------------

    Run the following command to see which files were modified by a
    particular commit:

    # git show --stat <commit hash>

    Or visit the following URL, replacing NNNNNN with the hash:

    <URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>

    To determine the commit count in a working tree (for comparison against
    nNNNNNN in the table above), run:

    # git rev-list --count --first-parent HEAD

    VII. References

    <URL:https://www.cve.org/CVERecord?id=CVE-2026-58094>

    The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-26:63.posixshm.asc> -----BEGIN PGP SIGNATURE-----

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