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Authentication bypass via JWT/OIDC userinfo cache key collision in LiteLLM
CVE-2026-35030 is an authentication bypass vulnerability in LiteLLM affecting versions prior to 1.83.0. In deployments where JWT authentication is enabled, the OIDC userinfo cache derives its cache key from only the first 20 characters of the presented token. Because JWTs generated with the same signing algorithm can share identical leading characters in their header portion, this truncated keying scheme can cause cache collisions between different tokens. An unauthenticated attacker can craft a token whose first 20 characters match those of a legitimate user token already present in the cache. If the cache lookup hits, LiteLLM associates the attacker with the cached userinfo for the legitimate user, resulting in impersonation and authorization under that user’s identity. The issue affects JWT/OIDC-enabled deployments and was corrected in LiteLLM 1.83.0.
What it means and what to do now: patch path, interim mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
Successful exploitation allows an unauthenticated attacker to bypass authentication and inherit the identity and permissions of a legitimate cached user. This can result in unauthorized access to protected LiteLLM functionality and any downstream actions or data access permitted to the impersonated account. The vulnerability primarily compromises authentication and authorization integrity rather than service availability.
If you can’t patch tonight, do this now.
If immediate upgrade is not possible, disable JWT/OIDC authentication paths that rely on the vulnerable userinfo cache, including configurations using enable_jwt_auth: true, until a fixed version can be deployed. Reducing or disabling the affected cache behavior and limiting exposure of JWT-authenticated endpoints can reduce risk, but upgrading remains the definitive mitigation.
Patch, then assume compromise.
Upgrade LiteLLM to version 1.83.0 or later, which fixes the unsafe cache key derivation used by the OIDC userinfo cache. Where LiteLLM is bundled within another product or distribution, apply the vendor-provided package update that includes a fixed LiteLLM release.
1 exploit validated by Mallory's analysis.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
4 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.