vulnerability / NVI-00011703 / Revision 1
agent-router: MCP session resume does not verify the embedded anti-hijacking subject; default Helm seed makes session IDs forgeable
GitHub lists this reviewed advisory for github.com/envoyproxy/ai-gateway. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
github.com/envoyproxy/ai-gateway
source listed>= 0.4.0-rc1, < 1.2.0-rc1
## Summary The MCP proxy's client-facing session ID embeds the authenticated caller's subject (JWT `sub` claim) specifically as an anti-hijacking discriminator — matching the Model Context Protocol specification's documented session-hijacking guidance (https://modelcontextprotocol.io/specification/2025-06-18/basic/security_best_practices#session-hijacking). However, the session-resume path never checks that discriminator against the current caller's identity, so any client that obtains a session ID (its own or another user's) can resume that session and act with it — including on routes with per-user backend sessions. This is aggravated by the official Helm chart shipping a literal, publicly known default seed (`"default-insecure-seed"`) for the key that encrypts these session IDs. ## Impact An attacker who obtains (or, under the default seed, forges) another user's `Mcp-Session-Id` value can resume that user's MCP session against the backend MCP server(s) bound to the route — reading conversation/tool-call state and invoking further JSON-RPC methods (e.g. `tools/call`, `resources/read`) in the context of that other user's already-initialized backend session. On a multi-tenant A
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
A fixed release is not deployment evidence.
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04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
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- GHSA-953h-535j-jg2v ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
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