CVE-2026-105922: 
NixOS vulnerability analysis and mitigation

CVE-2026-105922 is a denial-of-service vulnerability in vllm-project vLLM affecting all versions up to and including 0.31.0. The flaw resides in the get_token_bin_counts_and_mask function within vllm/model_executor/layers/utils.py (the Penalty Handler component), and can be triggered remotely by an authenticated user. It was disclosed on October 6, 2026, with a public proof-of-concept exploit available at the time of disclosure. It carries a CVSS v3.1 base score of 4.3 (Medium) and a CVSS v4.0 base score of 2.1 (Low) (GitHub Advisory, Feedly).

The root cause is classified as CWE-404 (Improper Resource Shutdown or Release) and CWE-248 (Uncaught Exception). When a vLLM server is started with --enable-prompt-embeds, the InputBatch.add_request method never writes prompt token IDs for prompt_embeds requests (only setting is_token_ids=False), leaving those rows in token_ids_cpu uninitialized or containing stale data from previously reused request slots. The _make_prompt_token_ids_cpu_tensor() function subsequently copies these uninitialized positions, and get_token_bin_counts_and_mask passes them to a CUDA scatter_add_ operation without consulting is_token_ids. When a batch contains prompt_embeds requests of mixed lengths — specifically when the longest prompt is an embedding request — the stale token IDs used as scatter indices can fall outside the valid range [0, vocab_size], triggering a CUDA device-side assertion (scatter gather kernel index out of bounds) that kills the EngineCore process (GitHub Issue #57719, PoC Gist).

Successful exploitation causes the vLLM EngineCore process to crash with a fatal CUDA error, rendering the entire inference server unresponsive — all in-flight and subsequent requests return HTTP 500 EngineDeadError and the server must be manually restarted. The impact is limited to availability; there is no confidentiality or integrity impact. Any client with API access to a server running with --enable-prompt-embeds can trigger this condition with a single burst of concurrent requests, making it a practical denial-of-service against shared or multi-tenant LLM serving deployments (GitHub Issue #57719, GitHub Advisory).

A public proof-of-concept exploit script (repro_prompt_embeds_penalties_engine_crash.py) was published by the original reporter at the time of disclosure and is referenced in the GitHub advisory (PoC Gist). The EPSS score is approximately 0.303% (21st percentile), indicating a low but non-negligible probability of exploitation in the wild. No active in-the-wild exploitation or threat actor attribution has been reported, and the vulnerability is not listed in the CISA KEV catalog. Exploitation requires low privileges (authenticated API access) but no special configuration beyond the server being started with --enable-prompt-embeds (GitHub Advisory, Feedly).

1. Identify a vulnerable target: Locate a vLLM server (version ≤ 0.31.0) started with the --enable-prompt-embeds flag and accessible over the network. Obtain valid API credentials (low-privilege access is sufficient).
2. Obtain model embedding weights: Retrieve the target model's embed_tokens.weight tensor from the Hugging Face cache or model files using safetensors.
3. Craft malicious requests: Construct at least two groups of /v1/completions requests using prompt_embeds (base64-encoded torch.save of embedding rows) with different prompt lengths — e.g., 900 tokens and 300 tokens — ensuring the longer group uses prompt_embeds. Include any penalty parameter (repetition_penalty, presence_penalty, or frequency_penalty) in each request body.
4. Send concurrent burst: Dispatch ~16 concurrent HTTP POST requests to /v1/completions with the crafted bodies, mixing the two prompt lengths so the longest prompt in the batch is a prompt_embeds request.
5. Engine crash: The mixed-length batch causes get_token_bin_counts_and_mask to scatter stale/uninitialized token IDs from reused request slots, triggering a CUDA out-of-bounds assertion that kills EngineCore. All subsequent requests return HTTP 500 EngineDeadError until the server is restarted (GitHub Issue #57719, PoC Gist).

• Logs: CUDA device-side assertion errors in server logs: ScatterGatherKernel.cu:203: Assertion 'idx_dim >= 0 && idx_dim < index_size && "scatter gather kernel index out of bounds"' failed; log entries showing EngineCore encountered a fatal error and vllm.v1.engine.exceptions.EngineDeadError.
• Network: Burst of concurrent POST requests to /v1/completions with prompt_embeds fields of varying sizes and penalty parameters (repetition_penalty, presence_penalty, frequency_penalty) set; subsequent requests returning HTTP 500 responses.
• Process: vLLM EngineCore worker process terminating unexpectedly; /health endpoint returning non-200 responses after a burst of prompt_embeds requests; torch.AcceleratorError: CUDA error: device-side assert triggered in process output (GitHub Issue #57719).

The primary remediation is to upgrade vLLM to a version beyond 0.31.0, where a bugfix (commit 37a52fa) addressing the is_token_ids-unaware scatter in the penalty bin-count builder has been merged (GitHub Issue #57719, GitHub Advisory). As an immediate workaround, disable the --enable-prompt-embeds server flag if it is not required for your use case, as the vulnerability only manifests when this feature is active. Additionally, implement network access controls to restrict API access to trusted clients only, and consider rate-limiting concurrent requests to reduce the attack surface until a patched version is deployed.

The vulnerability was originally reported by researcher Yunzez via a GitHub issue on September 19, 2026, with a detailed root cause analysis and a self-contained reproducer script (GitHub Issue #57719). A vLLM maintainer (vadiklyutiy) initially could not reproduce the issue on a nightly build but confirmed the underlying code defect was present; the reporter subsequently confirmed reproduction on released v0.27.1 and v0.30. A fix was committed by Cross2pro on September 27, 2026, and the CVE was formally published on October 6, 2026. No significant broader media coverage or social media discussion has been observed beyond the GitHub issue thread.