CVE-2026-49856 is a medium-severity server-side request forgery (SSRF) vulnerability in @jshookmcp/jshook (npm), affecting versions = 0.3.1. It is fixed in 0.3.2.
Summary The network domain has a central SSRF authorization policy that blocks private, loopback, link-local, and reserved targets unless an explicit authorization object allows private network access. The policy is enforced by raw HTTP/TCP/TLS RTT tools, but the ICMP probe and traceroute tools resolve the target and invoke the native ICMP/traceroute sink directly. An MCP client with access to an active network domain can therefore ask the jshookmcp server to probe internal addresses such as 10.0.0.1 even when local SSRF access is disabled for the other raw network tools. This exposes an internal reachability and route mapping primitive from the server network position. Affected code Current main https://github.com/vmoranv/jshookmcp/commit/d309c395738638e384c28c0f599b47b2213ab595 and npm package @jshookmcp/jshook 0.3.1 both contain the issue. src/server/domains/network/handlers/raw-latency-handlers.ts:61-66: networkrttmeasure parses optional authorization and calls resolveAuthorizedTransportTarget before probing. src/server/domains/network/handlers/raw-latency-handlers.ts:185-190: networklatencystats uses the same authorization guard. src/server/domains/network/handlers/raw-latency-handlers.ts:123-139: networktraceroute resolves target with resolveHostname and calls traceroute without an authorization policy check. src/server/domains/network/handlers/raw-latency-handlers.ts:240-257: networkicmpprobe resolves target with resolveHostname and calls icmpProbe without an authorization policy check. src/server/domains/network/handlers/raw-latency-handlers.ts:408-416: resolveHostname returns IPv4 literals directly and otherwise performs DNS A lookup without checking private, loopback, link-local, or reserved ranges. src/utils/network/ssrf-policy.ts:244-316: the central policy blocks private targets unless explicit authorization or ALLOWLOCALSSRF=true is set. Reproduction Used a focused regression test against the real handleCallTool and RawHandlers call path with fake native ICMP and policy sinks. The test does not send external traffic. It proves the denied control and the bypass through the same MCP meta-tool dispatch path. Test file path in my local checkout: Relevant test body: Command run: Result: The observed vulnerable call sequence is: resolveAuthorizedTransportTarget is not called on this path. The same missing policy pattern exists for networktraceroute. Impact An MCP client with access to the active network domain can use the server as a backend-origin internal network probing oracle. The result can reveal whether internal hosts respond, approximate latency, traceroute hops, and ICMP error classes from the server network position. The practical impact is strongest when jshookmcp is exposed over Streamable HTTP or another remote transport, multiple clients share one server, or the server runs on Windows or with raw socket capability. This is not code execution and does not by itself exfiltrate response bodies. Remediation Apply the same authorization model used by networkrttmeasure and networklatencystats to networkicmpprobe and networktraceroute. In particular, accept an optional authorization object, resolve the target through the central policy helper or an equivalent host-only policy helper, block private and reserved ranges by default, and pass only the policy-approved resolved address to the native probe. Add regression tests for default-denied private targets, authorized private CIDR access, private hostnames, and calltool dispatch.
Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.
CVE-2026-49856 has a CVSS score of 4.3 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (0.3.2). Upgrading removes the vulnerable code path.
npm
@jshookmcp/jshook (= 0.3.1)@jshookmcp/jshook → 0.3.2 (npm)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Already deployed Kodem? See CVE-2026-49856 in your environment →Upgrade @jshookmcp/jshook to 0.3.2 or later to resolve this vulnerability.
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CVE-2026-49856 is a medium-severity server-side request forgery (SSRF) vulnerability in @jshookmcp/jshook (npm), affecting versions = 0.3.1. It is fixed in 0.3.2. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
CVE-2026-49856 has a CVSS score of 4.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
@jshookmcp/jshook (npm) versions = 0.3.1 is affected.
Yes. CVE-2026-49856 is fixed in 0.3.2. Upgrade to this version or later.
Whether CVE-2026-49856 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
Upgrade @jshookmcp/jshook to 0.3.2 or later.