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Time-of-check Time-of-use (TOCTOU) Race Condition


Severity Medium
Score 6.1/10


An Allocation of Resources Without Limits or Throttling weakness in the memory management of the Packet Forwarding Engine (PFE) on Juniper Networks Junos OS Evolved PTX10003 Series devices allows an adjacently located attacker who has established certain preconditions and knowledge of the environment to send certain specific genuine packets to begin a Time-of-check Time-of-use (TOCTOU) Race Condition attack which will cause a memory leak to begin. Once this condition begins, and as long as the attacker is able to sustain the offending traffic, a Distributed Denial of Service (DDoS) event occurs. As a DDoS event, the offending packets sent by the attacker will continue to flow from one device to another as long as they are received and processed by any devices, ultimately causing a cascading outage to any vulnerable devices. Devices not vulnerable to the memory leak will process and forward the offending packet(s) to neighboring devices. Due to internal anti-flood security controls and mechanisms reaching their maximum limit of response in the worst-case scenario, all affected Junos OS Evolved devices will reboot in as little as 1.5 days. Reboots to restore services cannot be avoided once the memory leak begins. The device will self-recover after crashing and rebooting. Operator intervention isn't required to restart the device. This issue affects: Juniper Networks Junos OS Evolved on PTX10003: All versions prior to 20.4R3-S4-EVO; 21.3 versions prior to 21.3R3-S1-EVO; 21.4 versions prior to 21.4R2-S2-EVO, 21.4R3-EVO; 22.1 versions prior to 22.1R1-S2-EVO, 22.1R2-EVO; 22.2 versions prior to 22.2R2-EVO. To check memory, customers may VTY to the PFE first then execute the following show statement: show jexpr jtm ingress-main-memory chip 255 | no-more Alternatively one may execute from the RE CLI: request pfe execute target fpc0 command "show jexpr jtm ingress-main-memory chip 255 | no-more" Iteration 1: Example output: Mem type: NH, alloc type: JTM 136776 bytes used (max 138216 bytes used) 911568 bytes available (909312 bytes from free pages) Iteration 2: Example output: Mem type: NH, alloc type: JTM 137288 bytes used (max 138216 bytes used) 911056 bytes available (909312 bytes from free pages) The same can be seen in the CLI below, assuming the scale does not change: show npu memory info Example output: FPC0:NPU16 mem-util-jnh-nh-size 2097152 FPC0:NPU16 mem-util-jnh-nh-allocated 135272 FPC0:NPU16 mem-util-jnh-nh-utilization 6

  • HIGH
  • NONE
  • NONE
  • NONE
  • NONE
  • HIGH

CWE-367 - Time-of-check Time-of-use (TOCTOU) Race Condition

The software checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. This can cause the software to perform invalid actions when the resource is in an unexpected state.


Advisory Timeline

  • Published