CVE-2026-49429: The ZFS_IOC_USERSPACE_MANY ioctl, used by zfs-userspace(8), truncated a 64-bit output buffer size to a 32-bit

Routine

HIGH 7.8MITIGATE

CVE-2026-49429 is a high-severity flaw (CVSS 7.8) affecting freebsd. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The ZFS_IOC_USERSPACE_MANY ioctl, used by zfs-userspace(8), truncated a 64-bit output buffer size to a 32-bit integer for the kernel allocation, but used the original 64-bit size as the buffer limit when writing records. A local user with the "userused" delegated ZFS permission can trigger a kernel heap overflow via the ZFS_IOC_USERSPACE_MANY ioctl, potentially escalating privileges.

Why this priority

High severity

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 96%)
CISA exploited list	No
Weakness	CWE-122
Published	2026-08-19
Last modified	2026-09-01

Publisher (CNA): FreeBSD · Vendor: freebsd

Last updated 2026-09-01 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-19 06:17 UTCPublished CVE record published
2026-09-01 20:05 UTCUpdated Record last modified

freebsd freebsd MITIGATE

Affected: 14.3 · 14.3 p1 · 14.3 p10 · 14.3 p11 · 14.3 p12 · 14.3 p13 · 14.3 p14 · 14.3 p15

Fixed in: no fixed release known

Safe to downgrade to: a release before 14.3

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-49429?

freebsd: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-49429 being exploited?

CVE-2026-49429 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-49429 affect?

CVE-2026-49429 affects freebsd. Severity is high (CVSS 7.8). The ZFS_IOC_USERSPACE_MANY ioctl, used by zfs-userspace(8), truncated a 64-bit output buffer size to a 32-bit integer for the kernel allocation, but used the original 64-bit size as the buffer limit when writing records. A local user with

How urgent is CVE-2026-49429?

Priority 28/100. High severity

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References

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