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CVE-2026-47427

GitHub MCP Server: Nil Pointer Dereference DoS in completion/complete Handler

7.5 HighFix available

GitHub MCP Server is GitHub's official MCP Server. Prior to 1.1.0, the CompletionsHandler function in pkg/github/server.go accesses params.Ref without first checking whether it is nil, so a completion/complete request with a missing or empty ref field triggers a nil pointer dereference and a Go runtime panic; because the crash occurs before any authentication or token validation, any unauthenticated client able to send JSON-RPC messages can crash the server, resulting in a complete denial of service. This issue is fixed in version 1.1.0.

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
None
Integrity
None
Availability
High

Exploit likelihood

0.77%Up 0.4 points since Jul 29, 2026
90%50%10%1%

What each source reports

CVE List Score used 7.5

GitHub MCP Server: Nil Pointer Dereference DoS in completion/complete Handler

GitHub MCP Server is GitHub's official MCP Server. Prior to 1.1.0, the CompletionsHandler function in pkg/github/server.go accesses params.Ref without first checking whether it is nil, so a completion/complete request with a missing or empty ref field triggers a nil pointer dereference and a Go runtime panic; because the crash occurs before any authentication or token validation, any unauthenticated client able to send JSON-RPC messages can crash the server, resulting in a complete denial of service. This issue is fixed in version 1.1.0.

Record
CVE-2026-47427
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-476
Updated
2026-11-02
EUVDEUVD-2026-49875 7.5

GitHub MCP Server is GitHub's official MCP Server. Prior to 1.1.0, the CompletionsHandler function in pkg/github/server.go accesses params.Ref without first checking whether it is nil, so a completion/complete request with a missing or empty ref field triggers a nil pointer dereference and a Go runtime panic; because the crash occurs before any authentication or token validation, any unauthenticated client able to send JSON-RPC messages can crash the server, resulting in a complete denial of service. This issue is fixed in version 1.1.0.

Record
EUVD-2026-49875
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
GitHub AdvisoriesGHSA-w4q6-qw23-4rg7 7.5

GitHub MCP Server has Nil Pointer Dereference DoS in completion/complete Handler

Summary

A nil pointer dereference vulnerability in the GitHub MCP Server causes it to crash when receiving a malformed completion/complete request with missing or empty parameters. This allows any unauthenticated client to cause a complete denial of service.

Details

The CompletionsHandler function in pkg/github/server.go:198 accesses params.Ref without checking if it's nil first. When a client sends a completion/complete request with a missing ref field, the handler dereferences nil and the Go runtime panics.

The crash occurs before any authentication or token validation, so even requests with fake tokens can trigger it.

PoC

After completing the MCP initialization handshake, send either:

Empty params:

{"jsonrpc":"2.0","id":2,"method":"completion/complete","params":{}}

Missing ref field:

{"jsonrpc":"2.0","id":2,"method":"completion/complete","params":{"argument":{"name":"x","value":"y"}}}

Result:

panic: runtime error: invalid memory address or nil pointer dereference
goroutine 42 [running]:
github.com/github/github-mcp-server/pkg/github.NewMCPServer.CompletionsHandler.func1(...)
    pkg/github/server.go:198 +0x24

Impact

Any unauthenticated client that can send JSON-RPC messages to the server can crash it immediately. This is a complete denial of service - the panic is unrecoverable and kills the process.

Automated fuzzing with mcpsec found 108 crashes out of 925 test cases (11.7% crash rate).

Timeline

  • Feb 21, 2026 - Initial report sent to [email protected]
  • Mar 03, 2026 - Follow-up email sent, no response
  • Mar 21, 2026 - Re-verified on v0.33.0, sent detailed report with PoC, no response
  • Apr 06, 2026 - GHSA filed after 44 days without acknowledgment

Suggested Fix

func (s *Server) CompletionsHandler(ctx context.Context, params *mcp.CompleteParams) (*mcp.CompleteResult, error) {
    if params == nil || params.Ref == nil {
        return nil, fmt.Errorf("invalid request: missing ref parameter")
    }
    // ... rest of handler
}
Record
GHSA-w4q6-qw23-4rg7
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-476
Updated
2026-11-02
NVD 7.5

GitHub MCP Server is GitHub's official MCP Server. Prior to 1.1.0, the CompletionsHandler function in pkg/github/server.go accesses params.Ref without first checking whether it is nil, so a completion/complete request with a missing or empty ref field triggers a nil pointer dereference and a Go runtime panic; because the crash occurs before any authentication or token validation, any unauthenticated client able to send JSON-RPC messages can crash the server, resulting in a complete denial of service. This issue is fixed in version 1.1.0.

Record
CVE-2026-47427
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-476
Updated
2026-11-02
OSV 7.5

GitHub MCP Server: Nil Pointer Dereference DoS in completion/complete Handler

GitHub MCP Server is GitHub's official MCP Server. Prior to 1.1.0, the CompletionsHandler function in pkg/github/server.go accesses params.Ref without first checking whether it is nil, so a completion/complete request with a missing or empty ref field triggers a nil pointer dereference and a Go runtime panic; because the crash occurs before any authentication or token validation, any unauthenticated client able to send JSON-RPC messages can crash the server, resulting in a complete denial of service. This issue is fixed in version 1.1.0.

Record
CVE-2026-47427
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-476
Updated
2026-11-02
OSVGHSA-w4q6-qw23-4rg7 7.5

GitHub MCP Server has Nil Pointer Dereference DoS in completion/complete Handler

Summary

A nil pointer dereference vulnerability in the GitHub MCP Server causes it to crash when receiving a malformed completion/complete request with missing or empty parameters. This allows any unauthenticated client to cause a complete denial of service.

Details

The CompletionsHandler function in pkg/github/server.go:198 accesses params.Ref without checking if it's nil first. When a client sends a completion/complete request with a missing ref field, the handler dereferences nil and the Go runtime panics.

The crash occurs before any authentication or token validation, so even requests with fake tokens can trigger it.

PoC

After completing the MCP initialization handshake, send either:

Empty params:

{"jsonrpc":"2.0","id":2,"method":"completion/complete","params":{}}

Missing ref field:

{"jsonrpc":"2.0","id":2,"method":"completion/complete","params":{"argument":{"name":"x","value":"y"}}}

Result:

panic: runtime error: invalid memory address or nil pointer dereference
goroutine 42 [running]:
github.com/github/github-mcp-server/pkg/github.NewMCPServer.CompletionsHandler.func1(...)
    pkg/github/server.go:198 +0x24

Impact

Any unauthenticated client that can send JSON-RPC messages to the server can crash it immediately. This is a complete denial of service - the panic is unrecoverable and kills the process.

Automated fuzzing with mcpsec found 108 crashes out of 925 test cases (11.7% crash rate).

Timeline

  • Feb 21, 2026 - Initial report sent to [email protected]
  • Mar 03, 2026 - Follow-up email sent, no response
  • Mar 21, 2026 - Re-verified on v0.33.0, sent detailed report with PoC, no response
  • Apr 06, 2026 - GHSA filed after 44 days without acknowledgment

Suggested Fix

func (s *Server) CompletionsHandler(ctx context.Context, params *mcp.CompleteParams) (*mcp.CompleteResult, error) {
    if params == nil || params.Ref == nil {
        return nil, fmt.Errorf("invalid request: missing ref parameter")
    }
    // ... rest of handler
}
Record
GHSA-w4q6-qw23-4rg7
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-476
Updated
2026-11-02
OSVGO-2026-6118 No score

GitHub MCP Server has Nil Pointer Dereference DoS in completion/complete Handler in github.com/github/github-mcp-server

GitHub MCP Server has Nil Pointer Dereference DoS in completion/complete Handler in github.com/github/github-mcp-server

Record
GO-2026-6118
Updated
2026-11-02
OSVopenSUSE-SU-2026:21761-1 No score

Security update for govulncheck-vulndb

This update for govulncheck-vulndb fixes the following issues:

  • Update to version 0.0.20260827T195228 2026-08-27T19:52:28Z (jsc#PED-11136).

    Go CVE Numbering Authority IDs added or updated with aliases:

    • GO-2026-5026 CVE-2026-39821
    • GO-2026-6225
    • GO-2026-6250 CVE-2026-63328 GHSA-8rc5-4fr6-64pw
    • GO-2026-6253 CVE-2026-17106 GHSA-hfg8-hc9c-6c3h
    • GO-2026-6254 CVE-2026-53941 GHSA-vjhx-2cqw-3q6q
    • GO-2026-6255 CVE-2026-61711 GHSA-7236-3392-c5c6
    • GO-2026-6256 CVE-2026-61712 GHSA-72x6-4j93-7w86
    • GO-2026-6258 CVE-2026-45404 GHSA-42cj-99w8-cp2p
    • GO-2026-6259 CVE-2026-32637 GHSA-j2g6-362q-6qc6
    • GO-2026-6260 CVE-2026-55149 GHSA-qqff-5854-px68
    • GO-2026-6261 CVE-2026-54061 GHSA-rrwh-6jrq-wp5v
    • GO-2026-6262 GHSA-22w5-2fxg-vrwx
    • GO-2026-6263 CVE-2026-54168 GHSA-6f2p-296r-cc28
    • GO-2026-6264 CVE-2026-54245 GHSA-7q96-f8xw-jv5j
    • GO-2026-6265 GHSA-8fxq-53rx-ph5f
    • GO-2026-6266 CVE-2026-54167 GHSA-f5f4-3hh4-f54m
    • GO-2026-6267 GHSA-h58c-xccx-75m3
    • GO-2026-6268 GHSA-q9c5-pp7m-fm2g
    • GO-2026-6269 GHSA-rxhg-vcww-2mpw
    • GO-2026-6270 CVE-2026-54162 GHSA-x3g7-qrwc-f6c5
    • GO-2026-6271 CVE-2026-67448 GHSA-8r62-w5wh-fc5m
    • GO-2026-6272 CVE-2026-67447 GHSA-r553-m4fv-5v97
    • GO-2026-6273 CVE-2026-64679 GHSA-26w5-6g95-gj28
    • GO-2026-6274 CVE-2026-76905 GHSA-mmfr-pmjx-hw9w
    • GO-2026-6275 CVE-2026-77354 GHSA-xhj3-7xw9-vr34
    • GO-2026-6277 GHSA-4ph6-mjv7-3fq6
    • GO-2026-6278 GHSA-w67g-5rqw-f597
    • GO-2026-6279 CVE-2026-6046 GHSA-3vmp-whvv-5v9v
    • GO-2026-6280 CVE-2026-7387 GHSA-6hxm-w4hv-vgvw
    • GO-2026-6281 CVE-2026-6961 GHSA-8qq9-cqj8-82w4
    • GO-2026-6282 CVE-2026-7184 GHSA-9p44-r552-4wp9
    • GO-2026-6283 CVE-2026-6689 GHSA-c28q-m4gf-vg4q
    • GO-2026-6284 CVE-2026-55477 GHSA-jm48-m3rr-9hgg
    • GO-2026-6285 CVE-2026-6739 GHSA-m2w9-h2mm-79qr
    • GO-2026-6286 CVE-2026-3433 GHSA-rp4v-qc77-phm4
    • GO-2026-6287 GHSA-vx2m-jpxr-xv7w
    • GO-2026-6288 CVE-2026-11624 GHSA-76g7-m3xw-x9gr
    • GO-2026-6289 GHSA-w8j7-39hp-8x59
    • GO-2026-6290 CVE-2026-55581 GHSA-3x77-wg38-92r3
    • GO-2026-6291 CVE-2026-55582 GHSA-74hp-mggr-hv58
    • GO-2026-6292 CVE-2026-55580 GHSA-f5pj-2738-996m
    • GO-2026-6293 CVE-2026-55677 GHSA-vfp3-v2gw-7wfq
    • GO-2026-6294 CVE-2026-55092 GHSA-mcj4-mphf-j9ff
    • GO-2026-6295 CVE-2026-55637 GHSA-cmwv-wf9p-p8wx
    • GO-2026-6296 CVE-2026-54523 GHSA-79gf-7frw-68m9
    • GO-2026-6297 CVE-2026-50879 GHSA-g743-m6x3-v6wm
    • GO-2026-6298 CVE-2026-54563 GHSA-w5fv-7x5q-g8qp
    • GO-2026-6299 CVE-2026-50884 GHSA-5442-mh7f-72px
    • GO-2026-6300 CVE-2026-50891 GHSA-rcqf-cpv9-g5jf
    • GO-2026-6301 CVE-2026-42350 GHSA-g7gw-m874-7rmf

  • Update to version 0.0.20260819T170606 2026-08-19T17:06:06Z.

    Go CVE Numbering Authority IDs added or updated with aliases:

    • GO-2026-4720 GHSA-v3mg-9v85-fcm7
    • GO-2026-4942 CVE-2026-35172 GHSA-f2g3-hh2r-cwgc
    • GO-2026-4950
    • GO-2026-6093 GHSA-464c-974j-9xm6
    • GO-2026-6094 GHSA-gcjh-h69q-9w9g
    • GO-2026-6095 GHSA-r277-6w6q-xmqw
    • GO-2026-6097 CVE-2026-55495 GHSA-49h3-cwhj-4737
    • GO-2026-6098 CVE-2026-55496 GHSA-8r7f-r8hj-r3rv
    • GO-2026-6099 CVE-2026-57497 GHSA-g35j-m5xg-vh3q
    • GO-2026-6100 CVE-2026-55497 GHSA-g9j2-8w95-3vwv
    • GO-2026-6101 CVE-2026-55502 GHSA-hq88-5x99-x3gf
    • GO-2026-6102 CVE-2026-55499 GHSA-w8x7-h2px-xmq8
    • GO-2026-6103 CVE-2026-73564 GHSA-26gq-p25f-99cp
    • GO-2026-6104 CVE-2026-62323 GHSA-c3jm-gv5r-9wcp
    • GO-2026-6105 GHSA-c534-2w9c-x7fm
    • GO-2026-6106 GHSA-v6w6-358x-2433
    • GO-2026-6107 CVE-2026-73500 GHSA-6vch-q96h-7gc3
    • GO-2026-6108 CVE-2026-73505 GHSA-6xj8-qv9j-xcjq
    • GO-2026-6109 GHSA-86cx-wwf4-phq4
    • GO-2026-6110 CVE-2026-73509 GHSA-95cv-r8x4-vh75
    • GO-2026-6111 CVE-2026-73506 GHSA-fwjx-9p69-h25h
    • GO-2026-6112 CVE-2026-73502 GHSA-jpcw-4wr7-c3vq
    • GO-2026-6113 GHSA-p6ph-3jx2-3337
    • GO-2026-6114 CVE-2026-73499 GHSA-xg4h-6gfc-h4m8
    • GO-2026-6115 CVE-2026-56867
    • GO-2026-6117 GHSA-hp74-gm6m-2qm5
    • GO-2026-6118 CVE-2026-47427 GHSA-w4q6-qw23-4rg7
    • GO-2026-6119 CVE-2026-43983…
Record
openSUSE-SU-2026:21761-1
Updated
2026-11-02
OSVSUSE-SU-2026:23625-1 No score

Security update for govulncheck-vulndb

This update for govulncheck-vulndb fixes the following issues:

  • Update to version 0.0.20260827T195228 2026-08-27T19:52:28Z (jsc#PED-11136).

    Go CVE Numbering Authority IDs added or updated with aliases:

    • GO-2026-5026 CVE-2026-39821
    • GO-2026-6225
    • GO-2026-6250 CVE-2026-63328 GHSA-8rc5-4fr6-64pw
    • GO-2026-6253 CVE-2026-17106 GHSA-hfg8-hc9c-6c3h
    • GO-2026-6254 CVE-2026-53941 GHSA-vjhx-2cqw-3q6q
    • GO-2026-6255 CVE-2026-61711 GHSA-7236-3392-c5c6
    • GO-2026-6256 CVE-2026-61712 GHSA-72x6-4j93-7w86
    • GO-2026-6258 CVE-2026-45404 GHSA-42cj-99w8-cp2p
    • GO-2026-6259 CVE-2026-32637 GHSA-j2g6-362q-6qc6
    • GO-2026-6260 CVE-2026-55149 GHSA-qqff-5854-px68
    • GO-2026-6261 CVE-2026-54061 GHSA-rrwh-6jrq-wp5v
    • GO-2026-6262 GHSA-22w5-2fxg-vrwx
    • GO-2026-6263 CVE-2026-54168 GHSA-6f2p-296r-cc28
    • GO-2026-6264 CVE-2026-54245 GHSA-7q96-f8xw-jv5j
    • GO-2026-6265 GHSA-8fxq-53rx-ph5f
    • GO-2026-6266 CVE-2026-54167 GHSA-f5f4-3hh4-f54m
    • GO-2026-6267 GHSA-h58c-xccx-75m3
    • GO-2026-6268 GHSA-q9c5-pp7m-fm2g
    • GO-2026-6269 GHSA-rxhg-vcww-2mpw
    • GO-2026-6270 CVE-2026-54162 GHSA-x3g7-qrwc-f6c5
    • GO-2026-6271 CVE-2026-67448 GHSA-8r62-w5wh-fc5m
    • GO-2026-6272 CVE-2026-67447 GHSA-r553-m4fv-5v97
    • GO-2026-6273 CVE-2026-64679 GHSA-26w5-6g95-gj28
    • GO-2026-6274 CVE-2026-76905 GHSA-mmfr-pmjx-hw9w
    • GO-2026-6275 CVE-2026-77354 GHSA-xhj3-7xw9-vr34
    • GO-2026-6277 GHSA-4ph6-mjv7-3fq6
    • GO-2026-6278 GHSA-w67g-5rqw-f597
    • GO-2026-6279 CVE-2026-6046 GHSA-3vmp-whvv-5v9v
    • GO-2026-6280 CVE-2026-7387 GHSA-6hxm-w4hv-vgvw
    • GO-2026-6281 CVE-2026-6961 GHSA-8qq9-cqj8-82w4
    • GO-2026-6282 CVE-2026-7184 GHSA-9p44-r552-4wp9
    • GO-2026-6283 CVE-2026-6689 GHSA-c28q-m4gf-vg4q
    • GO-2026-6284 CVE-2026-55477 GHSA-jm48-m3rr-9hgg
    • GO-2026-6285 CVE-2026-6739 GHSA-m2w9-h2mm-79qr
    • GO-2026-6286 CVE-2026-3433 GHSA-rp4v-qc77-phm4
    • GO-2026-6287 GHSA-vx2m-jpxr-xv7w
    • GO-2026-6288 CVE-2026-11624 GHSA-76g7-m3xw-x9gr
    • GO-2026-6289 GHSA-w8j7-39hp-8x59
    • GO-2026-6290 CVE-2026-55581 GHSA-3x77-wg38-92r3
    • GO-2026-6291 CVE-2026-55582 GHSA-74hp-mggr-hv58
    • GO-2026-6292 CVE-2026-55580 GHSA-f5pj-2738-996m
    • GO-2026-6293 CVE-2026-55677 GHSA-vfp3-v2gw-7wfq
    • GO-2026-6294 CVE-2026-55092 GHSA-mcj4-mphf-j9ff
    • GO-2026-6295 CVE-2026-55637 GHSA-cmwv-wf9p-p8wx
    • GO-2026-6296 CVE-2026-54523 GHSA-79gf-7frw-68m9
    • GO-2026-6297 CVE-2026-50879 GHSA-g743-m6x3-v6wm
    • GO-2026-6298 CVE-2026-54563 GHSA-w5fv-7x5q-g8qp
    • GO-2026-6299 CVE-2026-50884 GHSA-5442-mh7f-72px
    • GO-2026-6300 CVE-2026-50891 GHSA-rcqf-cpv9-g5jf
    • GO-2026-6301 CVE-2026-42350 GHSA-g7gw-m874-7rmf

  • Update to version 0.0.20260819T170606 2026-08-19T17:06:06Z.

    Go CVE Numbering Authority IDs added or updated with aliases:

    • GO-2026-4720 GHSA-v3mg-9v85-fcm7
    • GO-2026-4942 CVE-2026-35172 GHSA-f2g3-hh2r-cwgc
    • GO-2026-4950
    • GO-2026-6093 GHSA-464c-974j-9xm6
    • GO-2026-6094 GHSA-gcjh-h69q-9w9g
    • GO-2026-6095 GHSA-r277-6w6q-xmqw
    • GO-2026-6097 CVE-2026-55495 GHSA-49h3-cwhj-4737
    • GO-2026-6098 CVE-2026-55496 GHSA-8r7f-r8hj-r3rv
    • GO-2026-6099 CVE-2026-57497 GHSA-g35j-m5xg-vh3q
    • GO-2026-6100 CVE-2026-55497 GHSA-g9j2-8w95-3vwv
    • GO-2026-6101 CVE-2026-55502 GHSA-hq88-5x99-x3gf
    • GO-2026-6102 CVE-2026-55499 GHSA-w8x7-h2px-xmq8
    • GO-2026-6103 CVE-2026-73564 GHSA-26gq-p25f-99cp
    • GO-2026-6104 CVE-2026-62323 GHSA-c3jm-gv5r-9wcp
    • GO-2026-6105 GHSA-c534-2w9c-x7fm
    • GO-2026-6106 GHSA-v6w6-358x-2433
    • GO-2026-6107 CVE-2026-73500 GHSA-6vch-q96h-7gc3
    • GO-2026-6108 CVE-2026-73505 GHSA-6xj8-qv9j-xcjq
    • GO-2026-6109 GHSA-86cx-wwf4-phq4
    • GO-2026-6110 CVE-2026-73509 GHSA-95cv-r8x4-vh75
    • GO-2026-6111 CVE-2026-73506 GHSA-fwjx-9p69-h25h
    • GO-2026-6112 CVE-2026-73502 GHSA-jpcw-4wr7-c3vq
    • GO-2026-6113 GHSA-p6ph-3jx2-3337
    • GO-2026-6114 CVE-2026-73499 GHSA-xg4h-6gfc-h4m8
    • GO-2026-6115 CVE-2026-56867
    • GO-2026-6117 GHSA-hp74-gm6m-2qm5
    • GO-2026-6118 CVE-2026-47427 GHSA-w4q6-qw23-4rg7
    • GO-2026-6119 CVE-2026-43983…
Record
SUSE-SU-2026:23625-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
github.com/github/github-mcp-server
Go
 before 1.1.0
1.1.0
govulncheck-vulndb
SUSE:Linux Enterprise Server 16.0
From an advisory covering 181 CVEs
 before 0.0.20260827T195228-160000.1.1
0.0.20260827T195228-160000.1.1
govulncheck-vulndb
SUSE:Linux Enterprise Server for SAP applications 16.0
From an advisory covering 181 CVEs
 before 0.0.20260827T195228-160000.1.1
0.0.20260827T195228-160000.1.1
govulncheck-vulndb
openSUSE:Leap 16.0
From an advisory covering 181 CVEs
 before 0.0.20260827T195228-160000.1.1
0.0.20260827T195228-160000.1.1

History

History
RecordedChangedSources
affected, facts
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

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

In short

CVE-2026-47427 is a high vulnerability (CVSS 7.5) in Github Mcp Server, published July 28, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.77%, the 55th percentile. Fixed in github.com/github/github-mcp-server 1.1.0.

References

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