CVE-2026-34756

MEDIUMPre-NVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 73% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Trending — 3 sources updated this week
6.5
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 6.5Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

vLLM is an inference and serving engine for large language models (LLMs). From 0.1.0 to before 0.19.0, a Denial of Service vulnerability exists in the vLLM OpenAI-compatible API server. Due to the lack of an upper bound validation on the n parameter in the ChatCompletionRequest and CompletionRequest Pydantic models, an unauthenticated attacker can send a single HTTP request with an astronomically large n value. This completely blocks the Python asyncio event loop and causes immediate Out-Of-Memory crashes by allocating millions of request object copies in the heap before the request even reaches the scheduling queue. This vulnerability is fixed in 0.19.0.

CVSS v3
6.5
EG Score
6.5(medium)
EG Risk
29(Track)
EG Risk 29/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity65% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
27.1%
KEV
Not listed

Published

April 6, 2026

Last Modified

July 15, 2026

Advisory Details (8)

Auto-updated Jul 7, 2026
Patch available. Sources: github, redhat, github_commit, github_pr.
redhat Patch Available
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34756.json
redhat

2455425 – (CVE-2026-34756) CVE-2026-34756 vllm: vLLM: Denial of Service via excessively large 'n' parameter in OpenAI-compatible API

https://bugzilla.redhat.com/show_bug.cgi?id=2455425
redhat Patch Available

cve-details

https://access.redhat.com/security/cve/CVE-2026-34756
redhat Patch Available
https://access.redhat.com/errata/RHSA-2026:36006
redhat Patch Available
https://access.redhat.com/errata/RHSA-2026:36005
github Patch Available

OOM Denial of Service via Unbounded `n` Parameter in OpenAI API Server · Advisory · vllm-project/vllm · GitHub

https://github.com/vllm-project/vllm/security/advisories/GHSA-3mwp-wvh9-7528
github_pr

fix(security): Add VLLM_MAX_N_SEQUENCES environment variable and enforce limit

Fix merged in vllm-project/vllm PR #37952 on 2026-03-27 — awaiting tagged release

https://github.com/vllm-project/vllm/pull/37952
github_commit

commit b111f8a61f10 (vllm-project/vllm)

Fix landed in vllm-project/vllm commit b111f8a61f10 — awaiting tagged release

https://github.com/vllm-project/vllm/commit/b111f8a61f100fdca08706f41f29ef3548de7380

Vendor Advisories for CVE-2026-34756(3)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFixed inDependents
vllm0.1.0 ... 0.9.2 (79 versions)0.19.0—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 9× in last 7d / 40× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-23 03:09 UTCEG score recompute
  2. 2026-07-22 14:08 UTCEPSS rescore
  3. 2026-07-21 15:24 UTCEPSS rescore
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  8. 2026-07-17 02:24 UTCOSV refresh
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  1. 2026-07-04 06:31 UTCEPSS rescore
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  70. 2026-05-20 18:54 UTCEG score recompute
  71. 2026-05-20 11:22 UTCEPSS rescore
  72. 2026-05-20 11:22 UTCEPSS rescore

Frequently asked(5)

What is CVE-2026-34756?
CVE-2026-34756 is a medium vulnerability published on April 6, 2026. vLLM is an inference and serving engine for large language models (LLMs). From 0.1.0 to before 0.19.0, a Denial of Service vulnerability exists in the vLLM OpenAI-compatible API server. Due to the lack of an upper bound validation on the n parameter in the ChatCompletionRequest and…
When was CVE-2026-34756 disclosed?
CVE-2026-34756 was first published in the National Vulnerability Database on April 6, 2026, with the most recent update on July 15, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-34756 actively exploited?
CVE-2026-34756 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 27.1% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-34756?
CVE-2026-34756 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-34756?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-34756, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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