CVE-2026-73564: CWE-129: Improper Validation of Array Index in fatedier frp
frp is a fast reverse proxy. From 0.53.0 until 0.70.1, frp's optional SSH Tunnel Gateway in pkg/ssh/server.go parses an SSH exec channel request by adding 4 to an attacker-controlled four-byte big-endian length. A length of 0xFFFFFFFF makes the uint32 addition wrap to 3, defeats the payload bounds check, and causes payload[4:3] to panic in TunnelServer.handleNewChannel. When no authorized-keys file is configured, sshConfig.NoClientAuth permits an unauthenticated peer to reach this channel phase before the frp token is checked, so a single five-byte request terminates the frps process and drops every active tunnel. This issue is fixed in version 0.70.1.
AI Analysis
Technical Summary
frp versions 0.53.0 through 0.70.0 contain a vulnerability in the SSH Tunnel Gateway component where an attacker-controlled four-byte big-endian length value is incremented by 4 without proper bounds checking. If the length is 0xFFFFFFFF, the addition wraps around to 3, bypassing payload bounds checks and causing a panic due to an invalid slice operation in TunnelServer.handleNewChannel. When no authorized-keys file is configured, unauthenticated peers can reach this vulnerable code path before token verification, allowing a crafted five-byte request to terminate the frps process and drop all active tunnels. This denial-of-service vulnerability is resolved in version 0.70.1.
Potential Impact
Successful exploitation results in a denial-of-service condition by crashing the frps process and dropping all active tunnels. The vulnerability can be triggered by unauthenticated attackers if no authorized-keys file is configured, making it remotely exploitable without privileges or user interaction.
Mitigation Recommendations
Upgrade frp to version 0.70.1 or later where this issue is fixed. Patch status is confirmed by the vendor stating the fix is in 0.70.1. Until upgrading, ensure an authorized-keys file is configured to prevent unauthenticated access to the vulnerable code path.
CVE-2026-73564: CWE-129: Improper Validation of Array Index in fatedier frp
Description
frp is a fast reverse proxy. From 0.53.0 until 0.70.1, frp's optional SSH Tunnel Gateway in pkg/ssh/server.go parses an SSH exec channel request by adding 4 to an attacker-controlled four-byte big-endian length. A length of 0xFFFFFFFF makes the uint32 addition wrap to 3, defeats the payload bounds check, and causes payload[4:3] to panic in TunnelServer.handleNewChannel. When no authorized-keys file is configured, sshConfig.NoClientAuth permits an unauthenticated peer to reach this channel phase before the frp token is checked, so a single five-byte request terminates the frps process and drops every active tunnel. This issue is fixed in version 0.70.1.
CVSS v4.0
Score 8.7high
Affected software
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
frp versions 0.53.0 through 0.70.0 contain a vulnerability in the SSH Tunnel Gateway component where an attacker-controlled four-byte big-endian length value is incremented by 4 without proper bounds checking. If the length is 0xFFFFFFFF, the addition wraps around to 3, bypassing payload bounds checks and causing a panic due to an invalid slice operation in TunnelServer.handleNewChannel. When no authorized-keys file is configured, unauthenticated peers can reach this vulnerable code path before token verification, allowing a crafted five-byte request to terminate the frps process and drop all active tunnels. This denial-of-service vulnerability is resolved in version 0.70.1.
Potential Impact
Successful exploitation results in a denial-of-service condition by crashing the frps process and dropping all active tunnels. The vulnerability can be triggered by unauthenticated attackers if no authorized-keys file is configured, making it remotely exploitable without privileges or user interaction.
Mitigation Recommendations
Upgrade frp to version 0.70.1 or later where this issue is fixed. Patch status is confirmed by the vendor stating the fix is in 0.70.1. Until upgrading, ensure an authorized-keys file is configured to prevent unauthenticated access to the vulnerable code path.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-08-12T20:53:46.380Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a7e058ebf8831d5399500ec
Added to database: 08/13/2026, 17:57:34 UTC
Last enriched: 08/13/2026, 18:11:33 UTC
Last updated: 08/13/2026, 19:10:58 UTC
Views: 4
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