High priorityDisclosed

Advisory · CVE-2026-103042

Unauthenticated memory exhaustion in LightLLM NCCL control channel

LightLLM through 1.2.0 lets unauthenticated attackers exhaust KV-transfer worker memory through the NCCL control channel's exposed_set_value method when started with --pd_trans_mode nccl, crashing workers and triggering node failure.

Advisory published September 30, 2026Independent summary
Vendor
ModelTC
Product
LightLLM
Identifier / CWE
CVE-2026-103042
CWE-770
Action timing
Immediate
ELI5

Explain it like I’m five

LightLLM's NCCL channel is a storage room with no limit on what gets shelved. A stranger keeps shoving junk in until the room bursts and the whole worker collapses.

SIMPLIFIED_ATTACK_PATH04 STEPS
  1. 01NCCL transfer mode

    The LightLLM server is started with --pd_trans_mode nccl, enabling the NCCL control channel.

  2. 02Method exposed

    The channel exposes the set_value method to unauthenticated network clients.

  3. 03Unbounded storage

    The attacker calls the method repeatedly to store unbounded key-value pairs with no size limits.

  4. 04Memory exhaustion

    KV-transfer worker memory fills until the worker crashes, triggering node failure.

What happened

LightLLM through 1.2.0 contains a memory exhaustion vulnerability in the NCCL control channel when the server is started with --pd_trans_mode nccl. Unauthenticated attackers can call the exposed exposed_set_value method to store unbounded key-value pairs with no size limits, exhausting KV-transfer worker memory until the worker crashes and triggers node failure.

No patch release is documented in the disclosure at the time of writing; the advisory states only that LightLLM through 1.2.0 is affected.

What to do

  1. Inventory LightLLM deployments running with --pd_trans_mode nccl.
  2. Restrict network access to the NCCL control channel so it is not reachable from untrusted clients.
  3. Switch away from nccl transfer mode where operationally feasible until a fixed release is published.
  4. Upgrade to a fixed LightLLM release as soon as the vendor publishes one.
  5. Monitor KV-transfer worker memory and set alerts on abnormal growth as an early warning.

Management note

This is an unauthenticated availability attack against GPU inference capacity: no code execution, but repeated crashes of KV-transfer workers take nodes out of service. Network segmentation plus a mode change is a complete interim mitigation.