In the Linux kernel, the following vulnerability has been resolved: apparmor: mediate the implicit connect of TCP fast open sendmsg… (CVE-2026-63828)
A vulnerability in the Linux kernel's AppArmor security module allowed bypassing connect mediation when using TCP Fast Open with sendmsg(). This occurred because AppArmor only checked send permissions but not connect permissions for sendmsg() calls with MSG_FASTOPEN, enabling a confined task to open outbound TCP/MPTCP connections that would otherwise be denied. The issue has been resolved by adding explicit mediation of the implicit connect in these cases, aligning with fixes in SELinux and Tomoyo.
AI Analysis
Technical Summary
The Linux kernel vulnerability CVE-2026-63828 involved AppArmor's failure to mediate the implicit connect operation triggered by sendmsg()/sendto() calls using MSG_FASTOPEN. Since MSG_FASTOPEN combines connect and write operations by opening the connection in the SYN packet, AppArmor's check only for AA_MAY_SEND allowed bypassing connect restrictions. The fix adds mediation for the implicit connect when MSG_FASTOPEN is set and a destination is provided, by enhancing apparmor_socket_sendmsg() to call aa_sk_perm() directly. This approach mirrors similar fixes in SELinux and Tomoyo and explicitly covers TCP and MPTCP fast open cases.
Potential Impact
An attacker confined by an AppArmor profile that permits sending but denies connecting could bypass connect restrictions and open outbound TCP or MPTCP connections using TCP Fast Open. This undermines the intended network access controls enforced by AppArmor profiles, potentially allowing unauthorized network communication from confined processes.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The vulnerability has been resolved in the Linux kernel by adding explicit mediation of the implicit connect in AppArmor when MSG_FASTOPEN is used. Users should apply the relevant Linux kernel updates once available to ensure this fix is included.
In the Linux kernel, the following vulnerability has been resolved: apparmor: mediate the implicit connect of TCP fast open sendmsg… (CVE-2026-63828)
Description
A vulnerability in the Linux kernel's AppArmor security module allowed bypassing connect mediation when using TCP Fast Open with sendmsg(). This occurred because AppArmor only checked send permissions but not connect permissions for sendmsg() calls with MSG_FASTOPEN, enabling a confined task to open outbound TCP/MPTCP connections that would otherwise be denied. The issue has been resolved by adding explicit mediation of the implicit connect in these cases, aligning with fixes in SELinux and Tomoyo.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The Linux kernel vulnerability CVE-2026-63828 involved AppArmor's failure to mediate the implicit connect operation triggered by sendmsg()/sendto() calls using MSG_FASTOPEN. Since MSG_FASTOPEN combines connect and write operations by opening the connection in the SYN packet, AppArmor's check only for AA_MAY_SEND allowed bypassing connect restrictions. The fix adds mediation for the implicit connect when MSG_FASTOPEN is set and a destination is provided, by enhancing apparmor_socket_sendmsg() to call aa_sk_perm() directly. This approach mirrors similar fixes in SELinux and Tomoyo and explicitly covers TCP and MPTCP fast open cases.
Potential Impact
An attacker confined by an AppArmor profile that permits sending but denies connecting could bypass connect restrictions and open outbound TCP or MPTCP connections using TCP Fast Open. This undermines the intended network access controls enforced by AppArmor profiles, potentially allowing unauthorized network communication from confined processes.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The vulnerability has been resolved in the Linux kernel by adding explicit mediation of the implicit connect in AppArmor when MSG_FASTOPEN is used. Users should apply the relevant Linux kernel updates once available to ensure this fix is included.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-fvhv-v8p3-vrwq
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-63828"]
- Ecosystems
- []
- Database Specific Severity
- null
- Cvss Version
- null
Threat ID: 6a5d27ad2a4a8d598913125d
Added to database: 07/19/2026, 19:38:21 UTC
Last enriched: 07/19/2026, 20:18:17 UTC
Last updated: 07/20/2026, 17:26:47 UTC
Views: 11
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