Part 2: How Third-Party Developers Closed the tun0 Leak in AmneziaVPN on Android
Third-party developers have published a detailed technical breakdown of how they closed a long-standing VPN tunnel leak affecting AmneziaVPN on Android. The issue, first reported in issue #2457, allows applications excluded from the VPN tunnel to bind sockets directly to the tun0 interface and thereby learn the address of the VPN server.
The root cause lies in Linux kernel behavior on versions 5.7 and newer. When an excluded application calls setsockopt(SO_BINDTODEVICE, "tun0"), the kernel falls back to treating the destination as an on-link neighbor if no matching routing rule exists for the UID. This bypasses the UID-based split-tunneling rules installed by VpnService and addDisallowedApplication.
The fix introduces a packet filter that inspects every outbound packet read from the tunnel descriptor. For each new flow the filter calls ConnectivityManager.getConnectionOwnerUid through a JNI bridge to obtain the UID. If the returned UID is INVALID_UID or belongs to the VPN client itself, the packet is dropped. In exclude mode this single rule effectively blocks all bypass attempts because excluded applications are never reported as owners.
The implementation was added to both traffic paths inside AmneziaVPN. On the Xray path the check sits inside the gVisor stack before SOCKS connections are created. On the AmneziaWG path a lightweight hook was placed inside amneziawg-go immediately after packet padding, maintaining a small cache of UID decisions to avoid repeated JNI calls.
Performance measurements on Android 16 showed no measurable increase in connection latency at 5000 new flows per second. When disabled, the filter adds only a single atomic read per packet and contributes no code to non-Android builds.
The authors stress that they are not official maintainers and that the three submitted pull requests remain unmerged. A side-loaded test build is available for verification. The article concludes with an extensive list of remaining edge cases, including raw sockets, IPv6, tethering, and certain UDP behaviors, together with a checklist for other VPN clients wishing to implement similar protections.
Related articles
Security Week 2644: Active Exploitation of PHP2Shell Vulnerabilities Confirmed
PHP developers released patches for two critical vulnerabilities collectively known as PHP2Shell on October 20, affecting PHP 8.2 through 8.5 as well as older branches. The flaws allow unauthenticated remote code execution on affected servers, which power approximately 70 percent of websites. Despite expectations of immediate exploitation, confirmed attacks with working exploits only began on October 25. CrowdStrike noted technical difficulties in weaponizing the issues in real-world environments. Only one-fifth of top Russian websites had applied the fixes by October 25. Additional incidents included compromised eMudhra certificates, a critical GitLab flaw, and a 16-year-old Broadcom router vulnerability.
Positive Technologies Offers Up to 500,000 Rubles for Bypassing PT Application Firewall
Positive Technologies has expanded its Standoff Bug Bounty program to include rewards for bypassing its web application firewalls. Researchers can earn between 150,000 and 500,000 rubles for demonstrating practical bypasses against PT Application Firewall PRO and PT Application Firewall Cloud. The program targets the core protective mechanisms, including traffic filtering, attack detection rules, and the management layer used by administrators. Submissions must include reproducible attack scenarios that show how malicious requests can pass through undetected, rather than relying on scanner reports or theoretical findings. Reward amounts vary by severity and confirmed business impact, with critical issues in the PRO version paying up to 500,000 rubles. The company plans to use validated findings to strengthen detection rules and improve overall product resilience.
Tailscale SSH Vulnerability Allows Root Access via Unix Socket Redirection
A researcher identified flaws in Tailscale that let an attacker with existing SSH access on one node escalate to root privileges and move laterally across the network. Erica Windisch of Cyberdione Labs demonstrated the issues in lab conditions against Tailscale 1.104.2 and Headscale 0.29.5. The core problem stems from privileged operations performed by the tailscaled process when handling Unix socket redirection, granting an ordinary SSH session access to root-only resources. The researcher used the technique to interact with Docker and run elevated commands, and showed that broad access policies allow automated lateral movement in under a second. Additional issues include denial-of-service conditions and bypasses of certain restrictions. Recommendations include reviewing SSH policies and disabling unnecessary socket redirection, noting that Headscale 0.29.5 lacks an independent way to turn the feature off.
Critical CVE-2026-111497 Out-of-Bounds Write Flaw in Google Brotli Decoder Impacts Broad Range of Environments
A severe vulnerability has been identified in the Google-developed Brotli decoder used for decompressing data in web communications and other applications. The flaw, tracked as CVE-2026-111497, allows out-of-bounds writes when processing specially crafted compressed data, potentially enabling arbitrary code execution, information disclosure, or denial of service. It carries a CVSS v4.0 base score of 9.2 and is rated Critical. Google has released patched versions 1.2.1, 1.1.1, and 1.0.10 of the library. Node.js incorporated the fix in its updates, while Microsoft issued an out-of-band patch for .NET on October 25, 2026, to address the issue. The vulnerability affects any environment relying on the Brotli C implementation for data decompression.