How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.

363,159

Total vulnerabilities in the database

frp: Unauthenticated Remote Denial of Service in the frp SSH Tunnel Gateway via Integer Overflow — github.com/fatedier/frp

Improper Validation of Array Index

Summary

An integer-overflow vulnerability in the frp server's optional SSH Tunnel Gateway lets any unauthenticated remote attacker crash the entire frps process with a single five-byte message. When the gateway parses an SSH exec channel request in pkg/ssh/server.go, it adds a small constant to a four-byte length value taken directly from the request. Because that length is fully attacker-controlled, a value of 0xFFFFFFFF makes the addition wrap around to a tiny number, defeating the only bounds check and forcing an out-of-range slice. Go raises a panic that nothing recovers, so the whole server exits. In the default gateway mode SSH clients are not authenticated and the request is handled before any frp token is checked, so the crash is reachable pre-authentication. It carries no state and is trivially repeatable, turning one crash into a sustained outage that drops every tunnel for every user.

Details

The exec request payload is a four-byte big-endian length followed by that many command bytes, and the length field is fully attacker-controlled. The gateway computes the end of the command as 4 + length. The constant 4 takes the uint32 type of the length field, so 4 + 0xFFFFFFFF wraps modulo 2^32 to 3. The only guard compares the real payload size against this wrapped value, so a five-byte payload passes the test 5 < 3, and the slice runs from index 4 to index 3:

// pkg/ssh/server.go:315-319
end := 4 + binary.BigEndian.Uint32(req.Payload[:4])  // 4 + 0xFFFFFFFF wraps to 3
if len(req.Payload) &lt; int(end) {                     // 5 &lt; 3 is false, so it passes
    continue
}
extraPayload := string(req.Payload[4:end])           // payload[4:3] -&gt; panic

The handler runs in a bare goroutine and no function in the call chain installs a recover, so the panic unwinds to the top of the goroutine and terminates the whole process rather than the single connection:

// pkg/ssh/server.go:226
go s.handleNewChannel(newChannel, extraPayloadCh)    // no recover anywhere in the chain

The sink is reachable without credentials in the default configuration. When no authorized-keys file is set, the gateway disables SSH client authentication, which is the default and documented mode where users authenticate through the frp token embedded in the SSH command. The exec request is processed during the channel phase, before that token is validated, so an unauthenticated peer reaches the sink:

// pkg/ssh/gateway.go:74
sshConfig.NoClientAuth = cfg.AuthorizedKeysFile == &quot;&quot;  // default: no client auth

Affected product: frp (fatedier), frps server, SSH Tunnel Gateway Affected versions: v0.53.0 (when the gateway was introduced) through v0.70.0, confirmed against a v0.70.0 build

PoC

The SSH Tunnel Gateway must be enabled with no authorized-keys file, which is the default mode of any deployment that turns the gateway on. No credentials and no knowledge of the target are required.

Enable the gateway on a stock v0.70.0 build:

bindPort = 7000

[sshTunnelGateway]
bindPort = 2200

As an unauthenticated SSH client, open a session channel and send one exec request whose four-byte length prefix is 0xFFFFFFFF followed by a single byte, giving the five-byte payload ff ff ff ff 41. The server immediately panics and exits:

panic: runtime error: slice bounds out of range [4:3]
...github.com/fatedier/frp/pkg/ssh.(*TunnelServer).handleNewChannel
    .../frp/pkg/ssh/server.go:319

The shell prompt returns in the server terminal, confirming the whole process has terminated and every other client tunnel is dropped at the same instant. A well-formed request of the same length (prefix 1) leaves the server running, proving the crash is caused by the overflow value and not by the exec request itself. The attacker can re-send the payload after any restart to hold the server down indefinitely.

Impact

This is an unauthenticated remote denial of service (CWE-190) leading to an out-of-range array index (CWE-129) and an unhandled process crash (CWE-755). A single five-byte, credential-free message kills the entire frps process. Because one frps commonly multiplexes the tunnels of many clients, the crash drops every active tunnel for every tenant at once and new logins are refused until the process is restarted, and re-sending the payload after each restart keeps the service down indefinitely (CWE-400). There is no confidentiality or integrity impact and no code execution.

This issue only affects frps instances with the SSH tunnel gateway explicitly enabled. The SSH tunnel gateway is disabled by default and is not commonly used in typical frps deployments. Default frps configurations are not affected.

Published: Jul 24, 2026
Updated: Jul 25, 2026
GHSA: GHSA-26gq-p25f-99cp
Severity: High
Exploit:
CISA KEV:

No technical information available.

CWEs:

Affected Software
References

Software	From	Fixed in
github.com/fatedier/frp	0.53.0	0.70.1

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.