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CVE-2026-59822

LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback

8.8 HighIn KEVPublic exploitFix available

LiteLLM is a proxy server (AI Gateway) to call LLM APIs in OpenAI (or native) format. Prior to 1.84.0, LiteLLM's MCP Streamable HTTP endpoint allowed an unauthenticated attacker to use a fabricated Authorization header to trigger an OAuth2 passthrough fallback path that replaced failed LiteLLM key validation with an empty UserAPIKeyAuth() object, allowing requests to reach MCP tooling without a valid LiteLLM key. This issue is fixed in version 1.84.0.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
Low
Availability
None

Exploit likelihood

0.84%Up 0.5 points since Jul 9, 2026
90%50%10%1%

What each source reports

CVE List Score used 8.8

LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback

LiteLLM is a proxy server (AI Gateway) to call LLM APIs in OpenAI (or native) format. Prior to 1.84.0, LiteLLM's MCP Streamable HTTP endpoint allowed an unauthenticated attacker to use a fabricated Authorization header to trigger an OAuth2 passthrough fallback path that replaced failed LiteLLM key validation with an empty UserAPIKeyAuth() object, allowing requests to reach MCP tooling without a valid LiteLLM key. This issue is fixed in version 1.84.0.

Record
CVE-2026-59822
CVSS 4.0
8.8 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-287, CWE-306
Updated
2026-11-02
EUVDEUVD-2026-42359 8.8

LiteLLM is a proxy server (AI Gateway) to call LLM APIs in OpenAI (or native) format. Prior to 1.84.0, LiteLLM's MCP Streamable HTTP endpoint allowed an unauthenticated attacker to use a fabricated Authorization header to trigger an OAuth2 passthrough fallback path that replaced failed LiteLLM key validation with an empty UserAPIKeyAuth() object, allowing requests to reach MCP tooling without a valid LiteLLM key. This issue is fixed in version 1.84.0.

Record
EUVD-2026-42359
CVSS 4.0
8.8 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-7488-6r32-c95q 8.8

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

Record
GHSA-7488-6r32-c95q
CVSS 4.0
8.8 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-287
Updated
2026-11-02
CISA KEV No score

BerriAI LiteLLM Improper Authentication Vulnerability

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.

Record
CVE-2026-59822
Weakness
CWE-287, CWE-306
Updated
2026-11-02
NVD 8.8

LiteLLM is a proxy server (AI Gateway) to call LLM APIs in OpenAI (or native) format. Prior to 1.84.0, LiteLLM's MCP Streamable HTTP endpoint allowed an unauthenticated attacker to use a fabricated Authorization header to trigger an OAuth2 passthrough fallback path that replaced failed LiteLLM key validation with an empty UserAPIKeyAuth() object, allowing requests to reach MCP tooling without a valid LiteLLM key. This issue is fixed in version 1.84.0.

Record
CVE-2026-59822
CVSS 4.0
8.8 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1
8.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
Weakness
CWE-287, CWE-306
Updated
2026-11-02
OSV 8.8

LiteLLM: MCP Authentication Bypass via OAuth2 Passthrough Fallback

LiteLLM is a proxy server (AI Gateway) to call LLM APIs in OpenAI (or native) format. Prior to 1.84.0, LiteLLM's MCP Streamable HTTP endpoint allowed an unauthenticated attacker to use a fabricated Authorization header to trigger an OAuth2 passthrough fallback path that replaced failed LiteLLM key validation with an empty UserAPIKeyAuth() object, allowing requests to reach MCP tooling without a valid LiteLLM key. This issue is fixed in version 1.84.0.

Record
CVE-2026-59822
CVSS 4.0
8.8 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-287, CWE-306
Updated
2026-11-02
OSVGHSA-7488-6r32-c95q 8.8

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

Record
GHSA-7488-6r32-c95q
CVSS 4.0
8.8 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
Weakness
CWE-287
Updated
2026-11-02
OSVPYSEC-2026-3479 8.8

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

Record
PYSEC-2026-3479
CVSS 4.0
8.8 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
litellm
PyPI
 before 1.84.0
1.84.0
litellm
PyPI
 before 1.84.0, plus listed versions
0.1.00.1.10.1.20.1.2010.1.202
Show 45 moreShow less
0.1.2030.1.2040.1.2050.1.2060.1.2070.1.2080.1.2090.1.2100.1.2110.1.2120.1.2130.1.2140.1.2150.1.2160.1.2170.1.2180.1.2190.1.2200.1.2210.1.2220.1.2230.1.2240.1.2250.1.2260.1.2270.1.2280.1.2290.1.22910.1.2300.1.2310.1.2320.1.2330.1.2340.1.2350.1.2360.1.2370.1.2380.1.30.1.310.1.320.1.3300.1.3310.1.340.1.3410.1.343
1.84.0
litellm
PyPI
 before 1.84.0, plus listed versions
0.1.00.1.10.1.20.1.2010.1.202
Show 45 moreShow less
0.1.2030.1.2040.1.2050.1.2060.1.2070.1.2080.1.2090.1.2100.1.2110.1.2120.1.2130.1.2140.1.2150.1.2160.1.2170.1.2180.1.2190.1.2200.1.2210.1.2220.1.2230.1.2240.1.2250.1.2260.1.2270.1.2280.1.2290.1.22910.1.2300.1.2310.1.2320.1.2330.1.2340.1.2350.1.2360.1.2370.1.2380.1.30.1.310.1.320.1.3300.1.3310.1.340.1.3410.1.343
1.84.0

Public exploits

Links only. Every CVE stores no exploit code.

Public exploits
SourceLinkDate
PoC in GitHubHORKimhab/CVE-2026-598222026-09-03

History

History
RecordedChangedSources
exploitation
first indexedCVE List, EUVD, GitHub Advisories, CISA KEV, NVD, OSV, PoC in GitHub

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-59822 is a high vulnerability (CVSS 8.8) in Berriai Litellm, published July 8, 2026. CISA lists it as known to be exploited, since September 2, 2026. EUVD reports exploitation since September 2, 2026. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 0.84%, the 57th percentile. Fixed in litellm 1.84.0.

References

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