Proxy bypass
Security incidents tagged Proxy bypass. Newest first.
1 Proxy bypass incident in the last 12 months
- Incidents
- 1
- Live
- 1
- Patched
- 0
- Days without an incident
- 0
- Longest quiet run: 79 days (Aug 17–Nov 3)
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- HighNo patch yet
mcp-go: JSON-RPC member-name case/Unicode folding lets calls bypass exact-match proxy allowlists (through v1.5.0, unpatched)
mark3labs/mcp-go's MCPServer.HandleMessage decodes JSON-RPC with encoding/json, which matches member names case-insensitively, folds ſ (U+017F) to s and K (U+212A) to k, and keeps the last of duplicate members. A request with Method/METHOD/paramſ, or with method given twice, still runs as the named call. mcp-go does not authorize calls itself, so this matters when a gateway or proxy in front allowlists method / params.name with an exact-match parser: the proxy may not see the call the server executes. The official Model Context Protocol Go SDK had the same class of bug (CVE-2026-27896 / GHSA-wvj2-96wp-fq3f) and fixed it in 1.3.1. Reported privately to contact@mark3labs.com on 2026-08-16 with no reply, then disclosed. Affected through v1.5.0 (tested on v1.0.0-beta.1, v1.4.0 and main after v1.5.0); no fix released. Workarounds: reject messages whose member names are not exactly the defined ones or that repeat a member, or re-encode before forwarding.
mcp-go (github.com/mark3labs/mcp-go)Since Nov 4, 2026
