CVE-2026-59822

BerriAI LiteLLM contains an improper authentication vulnerability in the MCP Streamable HTTP endpoint that could allow an unauthenticated attacker to establish an authenticated MCP session using an arbitrary Bearer token.

What this means for your business

It affects BerriAI LiteLLM. It matters if your company, or a supplier that handles your data, runs it.
Attackers are already using it. CISA added it to its list of flaws used in real attacks on 2 September 2026.
An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
FIRST's prediction model gives it a 0.9% chance of attack attempts being seen in the next 30 days, ranking above 56% of all known flaws.

What to do

1Check whether your company or your suppliers run BerriAI LiteLLM, and which version. The affected versions are listed further down this page.
2If you do, apply the vendor's fix. A patch or vendor advisory has been published.
3Treat it as urgent. US federal agencies must fix it by 16 September 2026. That deadline does not apply to private companies, but it shows how seriously CISA takes it.
4Because attackers have used it, check the affected systems for signs of a break-in, not only for the update.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

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Required action

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

CISA’s wording, unedited. The notes it mentions are in CISA’s catalogue entry.

Scoring

CVSS: 8.2 (v3.1)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
CVSS v4: 8.8
Weakness: CWE-287
Assigned by: security-advisories@github.com

Dates

Published: 2026-09-02
Last modified: 2026-09-03
Added to KEV: 2026-09-02
Remediation due: 2026-09-16
Sources: CISA KEV, NVD

Affected products

Litellm Litellm- 1.84.0

As listed in the NVD configuration data. Not a statement about your estate.