CVE-2026-40217

HighPublic PoCUpdated

Published: 10 April 2026

Published

10 April 2026

Modified

27 April 2026

KEV Added

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Patch

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CVSS Score 8.8 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS Score 0.0028 51.1th percentile

Risk Priority 18 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-40217 is a high-severity Unprotected Alternate Channel (CWE-420) vulnerability in Litellm Litellm. Its CVSS base score is 8.8 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked in the top 48.9% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified are NIST 800-53 CM-7 (Least Functionality) and SI-10 (Information Input Validation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190). What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

Directly remediates the bytecode rewriting vulnerability in LiteLLM by applying patches or upgrades as recommended in the x41-dsec advisory.

CM-7 Least Functionality good match

prevent

Prevents exploitation by configuring LiteLLM to disable the unnecessary /guardrails/test_custom_code URI and other non-essential functions.

SI-10 Information Input Validation good match

prevent

Blocks arbitrary code execution by validating and sanitizing all inputs submitted to the /guardrails/test_custom_code endpoint to prevent bytecode rewriting.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

Why these techniques?

The vulnerability allows remote code execution via a specific URI in LiteLLM, a network-exposed service, directly mapping to exploitation of public-facing applications.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

NVD Description

LiteLLM through 2026-04-08 allows remote attackers to execute arbitrary code via bytecode rewriting at the /guardrails/test_custom_code URI.

Deeper analysisAI

CVE-2026-40217 is a critical vulnerability in LiteLLM versions through 2026-04-08 that enables remote attackers to execute arbitrary code through bytecode rewriting at the /guardrails/test_custom_code URI. Classified under CWE-420, it carries a CVSS v3.1 base score of 8.8 (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H), indicating high severity due to its potential for significant impact across confidentiality, integrity, and availability.

The vulnerability can be exploited by remote attackers with low privileges over the network, requiring low attack complexity and no user interaction. Successful exploitation grants attackers the ability to execute arbitrary code on the affected system, potentially leading to full compromise including data theft, modification, or disruption of services.

The primary advisory from x41-dsec, available at https://www.x41-dsec.de/lab/advisories/x41-2026-001-litellm/, provides further details on the issue. Security practitioners should consult this reference for recommended mitigations and patches.