VulnerabilityPublished 27 Oct 2026

CVE-2026-94624: vllm p2p never connected zmq_exhaustion

Affects vllmSource GCVE Database

Authoritative record:CVE-2026-94624· High 8.7

Not known to be exploited · CVSS 8.7 High : upgrade to 0.32.0 soon.

Data as of 27 Oct 2026, 15:12 UTC

CVSS 4.0 base score

8.7High

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 0.32.0

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: High
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: High: There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Vulnerable System; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the Vulnerable System (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 21 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade vllm to 0.32.0.

Affected software

Product	Affected	Fixed in
PyPIvllm	Affected <0.32.0	Fixed in 0.32.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

### Summary When the `OffloadingConnector` uses `TieringOffloadingSpec` with a P2P secondary tier, an API client can submit many unique non-listening peer addresses through `kv_transfer_params.prefill`. vLLM keeps every never-established P2P session and its ZeroMQ sockets after the request finishes. On vLLM 0.26.0, 340 such peers filled the default ZeroMQ context socket quota; creating the next peer raised an uncaught `ZMQError`, terminated `EngineCore`, and shut down the API server. The path was reproduced with a normal API key and no access to the internal P2P listener. ### Details #### Root cause In vLLM 0.26.0, `P2PSecondaryTierManager.on_new_request()` reads the following request-controlled fields: ```json { "kv_transfer_params": { "prefill": { "kv_request_id": "id", "remote_host": "127.0.0.1", "remote_port": 49101 } } } ``` `on_new_request()` calls `_get_or_create_session(peer_id)`. This calls `ZmqTransport.connect()`, creates a `P2PSession`, and stores it in `_sessions` before the asynchronous ZeroMQ connection has been established. `ZmqTransport._open_connection()` creates a DEALER, enables a libzmq monitor, creates a PAIR socket for that monitor, calls `dealer.connect()`, and immediately stores the resulting `ZmqConnection` in `_connections`. Returning from `dealer.connect()` does not prove that the peer is reachable. The monitor subscribes only to `zmq.EVENT_DISCONNECTED`. A peer that never accepts the initial connection produced `EVENT_CONNECT_DELAYED`, `EVENT_CONNECT_RETRIED`, and `EVENT_CLOSED`, but no `EVENT_DISCONNECTED` during a 60-second observation. The production monitor therefore never calls `mark_dead()`, and `ZmqConnection.alive` remains true. Request completion calls `session.finish_request()`, but does not close or remove the peer session. The manager reaps only a session for which `session.connected and not session.alive` is true. A never-established peer remains `connected=True`, `alive=True`, and `ready=False`. There is no establishment deadline, idle eviction, or limit on pending or total peers. Each unique retained peer uses about three sockets in the same ZeroMQ context: the DEALER, the monitor endpoint created by libzmq, and the PAIR monitor client. With the measured default `MAX_SOCKETS=1023`, 340 peers use approximately 1,020 sockets in addition to the local ROUTER. The next peer fails while creating its monitor PAIR. The exception escapes through `on_new_request()` and the scheduler into the EngineCore loop: ```text P2PSecondaryTierManager._get_or_create_session() -> ZmqTransport.connect() -> ZmqTransport._open_connection() -> monitor_sock = self._zmq_ctx.socket(zmq.PAIR) -> zmq.error.ZMQError: Too many open files -> EngineDeadError ``` The process open-files limit was 65,536. The EngineCore had about 1,215 file descriptors at the failure point, so the failure was not the operating-system FD limit. #### Boundary and controls Each row below used a fresh vLLM process and pre-generated unique non-listening loopback ports. | Test | Result | |---|---| | Default `MAX_SOCKETS=1023`, 340 unique peers | 340 HTTP 200 responses; 340 active peers; service healthy | | Default limit, 344 unique peers, concurrency 4 | 340 HTTP 200 and 4 HTTP 500 responses; EngineCore and API exited | | Default limit, 344 unique peers, concurrency 1 | Same 340-peer ceiling and service exit | | Same endpoint repeated 512 times | 512 HTTP 200 responses; one active peer; service healthy | | 512 requests without P2P parameters | 512 HTTP 200 responses; no active peers; service healthy | A diagnostic A/B changed only the context `MAX_SOCKETS` value. Raising it from 1,023 to 2,048 moved the last fully successful point from 340 to 682 peers. The 683rd peer then raised the same `ZMQError` and terminated the service. The approximately 2.01x movement in the boundary identifies the ZeroMQ context quota as the exhausted resource. The failure runs used logging-only instrumentation around `_open_connection()` to record the context limit, peer count, and process FD count. It did not add or close any ZeroMQ socket and re-raised the original exception. #### Related public work [PR #47843](https://github.com/vllm-project/vllm/pull/47843) is an open, unmerged proposal that identifies client-supplied P2P peer addresses as an SSRF risk and proposes API sanitization plus a configured peer allowlist. Those changes would block this public API trigger, but the PR does not add a connection deadline, session cleanup, or a capacity limit for never-established peers. This report adds the deterministic resource-exhaustion and service-exit impact of the retained state. [PR #49823](https://github.com/vllm-project/vllm/pull/49823) fixes cleanup and reconnection after a connection has been marked dead. A peer that never establishes does not receive the subscribed `EVENT_DISCONNECTED` event, so it never enters that dead-state cleanup path. ### Impact This is uncontrolled resource

CWE-770Allocation of Resources Without Limits or Throttling (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #25
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
Requirements
Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
Architecture and Design
Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
Architecture and Design
Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
OWASP ASVS 4.0.3
V8.1.4 (opens in a new tab)
V13.4.1 (opens in a new tab)
V11.1.4 (opens in a new tab)
Attack patterns
XML Ping of the Death (opens in a new tab)
Exponential Data Expansion (opens in a new tab)
Serialized Data Parameter Blowup (opens in a new tab)
Serialized Data with Nested Payloads (opens in a new tab)
Oversized Serialized Data Payloads (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

WeaknessesCWE-770

Technical details

References

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