Vulnerability in @modelcontextprotocol/sdk (CVE-2026-0621)
Summary
Vulnerability in @modelcontextprotocol/sdk (CVE-2026-0621). Risk of unauthorized operations or information disclosure. Exploitable via UriTemplate. Mitigation: upgrade to 1.25.2 or later.
Original description
The description as published by the source.
Impact
A ReDoS vulnerability in the UriTemplate class allows attackers to cause denial of service. The partToRegExp() function generates a regex pattern with nested quantifiers (([^/]+(?:,[^/]+)*)) for exploded template variables (e.g., {/id*}, {?tags*}), causing catastrophic backtracking on malicious input.
Who is affected: MCP servers that register resource templates with exploded array patterns and accept requests from untrusted clients.
Attack result: An attacker sends a crafted URI via resources/read request, causing 100% CPU utilization, server hang/crash, and denial of service for all clients.
Affected Versions
All versions of @modelcontextprotocol/sdk prior to the patched release.
Patches
v1.25.2 contains b392f02ffcf37c088dbd114fedf25026ec3913d3 the fix modifies the regex pattern to prevent backtracking.
Workarounds
- Avoid using exploded patterns (
{/id*},{?tags*}) in resource templates - Implement request timeouts and rate limiting
- Validate URIs before processing to reject suspicious patterns
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-0621 has been found in @modelcontextprotocol/sdk.
Attackers can target a specific entry point like UriTemplate over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade @modelcontextprotocol/sdk to 1.25.2 or later.
If unsure, ask your IT team or search "@modelcontextprotocol/sdk CVE-2026-0621" on the vendor's site.
CVE-2026-0621 (@modelcontextprotocol/sdk) — CWE-1333 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: UriTemplate
Patched: 1.25.2 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-1333) exists in @modelcontextprotocol/sdk. Attackers reach the vulnerable code path via UriTemplate without authentication.
Check the vendor advisory for the affected versions of @modelcontextprotocol/sdk. Attack surface: UriTemplate.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 1.25.2.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r '@modelcontextprotocol/sdk' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r '@modelcontextprotocol/sdk' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
@modelcontextprotocol/sdkを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade @modelcontextprotocol/sdk to 1.25.2ステージング環境で 1.25.2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory disclosure@vulncheck.com
- exploit github.com
- web nvd.nist.gov
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com