CVE-2026-90100 ptp: netc: fix period truncation and potential divide-by-zero in PEROUT
A local attacker can trigger a divide-by-zero error in the Linux kernel NETC PTP driver, causing a system crash.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90100?
CVE-2026-90100 is a vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ptp: netc: fix period truncation and potential divide-by-zero in PEROUT
The max_period bound in net_timer_enable_perout() was computed as:
max_period = (u64)NETC_TMR_DEFAULT_FIPER + integral_period;
which exceeds U32_MAX when integral_period > 0 (e.g. 0x100000002 for the default 333333333 Hz clock). A period_ns that passes this check but exceeds U32_MAX is then silently truncated when stored into the u32 struct netc_pp::period field.
A truncated value of zero can reach netc_timer_set_perout_alarm(), where the local u32 period variable would also be 0, causing a divide-by-zero in roundup_u64(delta, period) whenever the stime < min_time branch is taken (which always happens for a start time of {0, 0}).
Additionally, netc_timer_enable_periodic_pulse() and netc_timer_enable_fiper() both compute:
fiper = pp->period - integral_period;
A zero pp->period results in an unsigned wraparound to 0xFFFFFFFD, mis-programming the FIPER hardware register.
Fix all three issues by capping max_period at NETC_TMR_DEFAULT_FIPER (0xFFFFFFFF). This ensures that any period_ns passing the range check fits in a u32 without truncation, so the stored value is always valid and non-zero. The accepted range is reduced by integral_period ns (typically only a few nanoseconds), which is negligible in practice.
Which versions are affected by CVE-2026-90100?
How do I fix CVE-2026-90100?
Apply the vendor's patch.
Is CVE-2026-90100 being exploited?
There is no known exploitation of CVE-2026-90100 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-90100, DEBIAN-CVE-2026-90100, GHSA-rpp5-w8v3-w64q, UBUNTU-CVE-2026-90100.