CVE-2026-5072 Overview
CVE-2026-5072 is a bitwise shift vulnerability in the Precision Time Protocol (PTP) subsystem of the Zephyr real-time operating system. A remote attacker on an adjacent network can send a crafted PTP_MSG_MANAGEMENT message to set an unvalidated negative log_announce_interval value in a port's data set. Subsequent processing of a PTP_MSG_ANNOUNCE message triggers an out-of-range bitwise shift, resulting in undefined behavior. The flaw is tracked under CWE-1335 (Incorrect Bitwise Shift of Integer).
Critical Impact
Exploitation can crash the Zephyr device through a compiler-emitted illegal instruction trap or cause resource starvation loops, producing a denial-of-service condition on embedded systems running the PTP stack.
Affected Products
- Zephyr Project RTOS PTP subsystem
- Embedded devices implementing IEEE 1588 PTP on Zephyr
- Networked Zephyr deployments exposing PTP management messages
Discovery Timeline
- 2026-05-22 - CVE-2026-5072 published to NVD
- 2026-05-26 - Last updated in NVD database
Technical Details for CVE-2026-5072
Vulnerability Analysis
The vulnerability resides in the PTP port timer logic. When the Zephyr PTP stack handles a PTP_MSG_ANNOUNCE message, the function port_timer_set_timeout_random computes a timeout using the expression NSEC_PER_SEC >> -log_seconds. The log_seconds value derives from log_announce_interval, which an attacker can control by sending a PTP_MSG_MANAGEMENT message. Because the field is not validated for negative values, the shift operand can become arbitrarily large.
The C language specification defines shift amounts greater than or equal to the operand width as undefined behavior. When the attacker supplies a value such as -127, the negated shift amount exceeds the 64-bit integer width. Compilers may emit code that triggers an illegal instruction trap on architectures such as ARM Cortex-M, halting the device.
On architectures where the shift silently wraps, the result is a zero or otherwise invalid timeout. This drives the announce timer into a tight resource-starvation loop, preventing the scheduler from servicing other tasks. The attack vector requires adjacent network access but no authentication or user interaction.
Root Cause
The root cause is missing input validation on the log_announce_interval field carried inside PTP management messages. The PTP subsystem accepts the signed value and stores it in the port data set without bounding checks. Downstream arithmetic then negates the value and uses it as a shift count, violating the precondition that shift counts remain non-negative and below the operand width.
Attack Vector
An attacker on the same Layer 2 segment as the target device crafts a PTP management message with an extreme negative log_announce_interval. Once the value is stored, any subsequent announce message processed by the port triggers the undefined shift. No prior authentication is required because PTP management messages are typically accepted from any peer on the network segment. See the GitHub Security Advisory GHSA-3v98-458v-388r for protocol-level details.
No verified public proof-of-concept code is available. The exploitation mechanism is described in prose only.
Detection Methods for CVE-2026-5072
Indicators of Compromise
- PTP management messages containing log_announce_interval values outside the IEEE 1588 valid range of -128 to 127, or any negative value below typical operational ranges such as -4.
- Unexpected device resets or watchdog-triggered reboots on Zephyr nodes participating in PTP synchronization.
- Sustained CPU saturation on a Zephyr node correlated with receipt of PTP announce traffic.
Detection Strategies
- Inspect PTP traffic on monitored segments using a packet analyzer and flag management messages that modify timing interval fields.
- Compare device uptime telemetry against baseline expectations to identify crash-restart cycles aligned with PTP message arrivals.
- Apply intrusion detection rules on PTP UDP ports 319 and 320 to identify malformed or out-of-range management TLVs.
Monitoring Recommendations
- Log all PTP management message sources and alert on senders that are not authorized grandmasters or boundary clocks.
- Monitor Zephyr device serial or syslog output for fault handler or hard fault traces following PTP traffic.
- Track ingress rates of PTP_MSG_MANAGEMENT frames per source MAC address to detect injection attempts.
How to Mitigate CVE-2026-5072
Immediate Actions Required
- Apply the Zephyr Project patch referenced in the GitHub Security Advisory GHSA-3v98-458v-388r and rebuild affected firmware images.
- Restrict PTP traffic to trusted VLANs and deny PTP management messages from untrusted hosts at the switch level.
- Audit deployed Zephyr images to identify devices with the PTP subsystem enabled in production builds.
Patch Information
The Zephyr Project has issued a fix in the PTP subsystem that validates the log_announce_interval field before storing it in the port data set and bounds the shift operand used by port_timer_set_timeout_random. Refer to the upstream advisory at zephyrproject-rtos/zephyr GHSA-3v98-458v-388r for the affected and fixed commit ranges.
Workarounds
- Disable the PTP subsystem in prj.conf by unsetting CONFIG_PTP if precise time synchronization is not required.
- Configure switches and routers to block UDP ports 319 and 320 from untrusted network segments.
- Use Access Control Lists to permit PTP messages only from known grandmaster MAC or IP addresses.
# Configuration example: disable PTP in a Zephyr build
# In your application's prj.conf
CONFIG_PTP=n
CONFIG_NET_GPTP=n
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
