🛡️ CVE-2026-59822 — litellm
Description
LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback
Impact
LiteLLM's MCP Streamable HTTP endpoint could allow an unauthenticated attacker to establish an authenticated MCP session using an arbitrary Bearer token.
The MCP auth handler supported OAuth2 passthrough for upstream MCP servers, but the fallback path could replace failed LiteLLM key validation with an empty UserAPIKeyAuth() object. This allowed requests with a fabricated Authorization header to reach MCP tooling without a valid LiteLLM key.
An attacker could use this to list and call configured MCP tools and access connected services exposed through MCP.
Patches
The issue is fixed in 1.84.0.
We recommend upgrading to 1.84.0 or later.
Workarounds
If upgrading is not immediately possible, disable MCP routes or block access to /mcp/ and related MCP endpoints at your reverse proxy or API gateway.
References
- [v1.84.0](https://github.com/BerriAI/litellm/releases/tag/v1.84.0)
How this vulnerability can be exploited
This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. Rated impact: confidentiality high, integrity low, availability none.
Weakness class
CVE-2026-59822 is classified as CWE-287: Improper Authentication. The identity of the caller is not established correctly, so an attacker can act as another user.
Affected software
CVE-2026-59822 is recorded against 1 package.
- litellm (fixed in 1.84.0)
Timeline and source
Published on 22 July 2026 and last revised on 23 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from OSV.
References
github.com (Web)
nvd.nist.gov (Advisory)
github.com (Web)
github.com (Web)
github.com (Package)
github.com (Web)
Details
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
Affected Packages
| Software | From version | Fixed in |
|---|---|---|
| litellm | — | 1.84.0 |
References
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More CVE 2026 advisories
Browse all of CVE 2026 in the advisory index.
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