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FreeBSD-EN-26:05.vm                                             Errata Notice
                                                          The FreeBSD Project

Topic:          The page fault handler fails to zero memory

Category:       core
Module:         vm
Announced:      2026-04-21
Affects:        All supported versions of FreeBSD.
Corrected:      2026-04-13 10:57:44 UTC (stable/15, 15.0-STABLE)
                2026-04-21 15:44:24 UTC (releng/15.0, 15.0-RELEASE-p6)
                2026-04-13 02:56:40 UTC (stable/14, 14.4-STABLE)
                2026-04-21 15:45:29 UTC (releng/14.4, 14.4-RELEASE-p2)
                2026-04-21 15:45:59 UTC (releng/14.3, 14.3-RELEASE-p11)
                2026-04-13 02:58:42 UTC (stable/13, 13.5-STABLE)
                2026-04-21 15:47:06 UTC (releng/13.5, 13.5-RELEASE-p12)

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

I.   Background

The mmap(2) system call allows applications and system libraries to allocate
heap memory using the MAP_ANON flag.  The system call allocates virtual memory
in the calling thread's address space and phyiscal memory is allocated on demand
as page faults occur.  Memory allocated this way is allocated to be zero-filled.

II.  Problem Description

Due to a regression introduced a previous erratum which attempted to fix a
similar problem, under some conditions, particularly heavy memory pressure with
swapping, the phyiscal pages allocated and mapped by the kernel may not be
zero-filled.

III. Impact

This bug has been observed to cause process crashes.

IV.  Workaround

No workaround is available.

V.   Solution

Upgrade your 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 system installed from base system packages:

Systems running a 15.0-RELEASE 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 now

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

Systems running a RELEASE version of FreeBSD on the amd64 or arm64 platforms,
or the i386 platform on FreeBSD 13, 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 now

3) To update your 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.

[FreeBSD 15.0]
# fetch https://security.FreeBSD.org/patches/EN-26:05/vm-15.patch
# fetch https://security.FreeBSD.org/patches/EN-26:05/vm-15.patch.asc
# gpg --verify vm-15.patch.asc

[FreeBSD 14.4 and 14.3]
# fetch https://security.FreeBSD.org/patches/EN-26:05/vm-14.patch
# fetch https://security.FreeBSD.org/patches/EN-26:05/vm-14.patch.asc
# gpg --verify vm-14.patch.asc

[FreeBSD 13.5]
# fetch https://security.FreeBSD.org/patches/EN-26:05/vm-13.patch
# fetch https://security.FreeBSD.org/patches/EN-26:05/vm-13.patch.asc
# gpg --verify vm-13.patch.asc

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

# cd /usr/src
# patch < /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/                              58718cf36593    stable/15-n282974
releng/15.0/                            ffb21713d9fd  releng/15.0-n281019
stable/14/                              9b7c0f4f81f0    stable/14-n273947
releng/14.4/                            1abe7ead45c3  releng/14.4-n273683
releng/14.3/                            4d22b3925df8  releng/14.3-n271483
stable/13/                              50f7b62f0862    stable/13-n259839
releng/13.5/                            6c9dd7528350  releng/13.5-n259209
- -------------------------------------------------------------------------

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://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294039>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-26:05.vm.asc>
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