mcpm · Model Context Protocol Python SDK: Server bearer-token authentication accepts tokens issued for a different resource
Affects mcpmSource GCVE Database
Not known to be exploited · CVSS 6.8 Medium.
Data as of 30 Oct 2026, 06:59 UTC
Thin evidence
One scorer or none| CNA (GitHub_M) | CVSS 3.1 | 6.8 |
|---|
- EPSS
- 0.3% chance of exploitation in 30 days – higher than 30% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:NExploitation evidence
Disclosed: evidence found.
CVE published 27 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Homebrewmcpmpkg:brew/mcpmOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
Description
### Summary In affected versions, the SDK's server-side bearer authentication had no way to check that a token was issued for your server (its audience). Where one authorization server issues tokens for several services, a valid token for another service was also accepted by your MCP server. ### Am I affected? Yes, if your HTTP server uses the SDK's bearer authentication (`auth=AuthSettings(...)` with `token_verifier=`), its authorization server also issues tokens for other services, and your `TokenVerifier` does not check the token's audience (`aud`) itself. Affected versions: - `mcp` 1.10.0 through 1.29.1 - `mcp` 2.0.0 through 2.1.1 ### Fix Upgrade to: - 1.x: `mcp` 1.30.0 or later - 2.x: `mcp` 2.2.0 or later **Upgrading alone changes nothing.** The patched versions add a `validate_token_resource` setting that is off unless you set it. To turn the check on, make both of these changes together: 1. Set `validate_token_resource=True` in `AuthSettings`, with `resource_server_url` set to the audience your authorization server puts in tokens for your server. 2. Return the token's audience from `verify_token()` as `AccessToken.resource`. A token for another service then gets `401`. With only the first change, every request gets `401`. If your `TokenVerifier` already checks the audience, set `validate_token_resource=False` to silence the deprecation warning. The setting will default to `True` in 3.0. If you cannot upgrade yet, reject any token whose `aud` does not include your server inside `verify_token()`. That closes the issue on every version.
References
- github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-w4fh-qvv9-3v23 (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/pull/3447 (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/pull/3451 (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/commit/0c9136841ff092987a20700ff9c2c9789bda2f40 (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/commit/8c2fa6eabacde869d75568e33b9d466b58c2f512 (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0 (opens in a new tab)
- github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0 (opens in a new tab)