CVE-2026-98550 — tipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

tipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow

Commit 48a5fe38772b ("tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG") rejected duplicate/stale ACKs in tipc_group_proto_rcv() by returning early when less_eq(acked, m->bc_acked).

However, that check remains incomplete in two ways:

1. When grp->bc_ackers is zero (e.g. on a quiet group, when replicast ACKs were not requested, or after all expected members have already acknowledged), an unexpected GRP_ACK_MSG with acked > m->bc_acked passes less_eq() and unconditionally decrements grp->bc_ackers. Because bc_ackers is a u16, this wraps to 65535, causing tipc_group_bc_cong() to permanently report congestion and blocking all future group broadcasts on the socket.

2. During an active broadcast round (grp->bc_ackers > 0), the sender transmits packet S and advances grp->bc_snd_nxt to S + 1. Receivers increment their expected counter to S + 1 upon consuming packet S, so the only valid ACK value for the current round is strictly acked == grp->bc_snd_nxt.

However, tipc_group_update_bc_members() initializes each member's m->bc_acked to prev = grp->bc_snd_nxt - 1 (S - 1 before increment). This leaves a 2-sequence gap (S - 1 to S + 1) in sequence space. An incoming ACK is therefore neither rejected as duplicate nor prevented from decrementing grp->bc_ackers if an unexpected or stale…

USN-8959-1 — linux, linux-aws, linux-gcp, linux-hwe-7.0, linux-ibm, linux-oracle vulnerabilities

Affected: Ubuntu:24.04:LTS: linux-hwe-7.0, Ubuntu:26.04:LTS: linux, Ubuntu:26.04:LTS: linux-aws, Ubuntu:26.04:LTS: linux-gcp, Ubuntu:26.04:LTS: linux-ibm, Ubuntu:26.04:LTS: linux-oracle

Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system. This update corrects flaws in the following subsystems: - USB Gadget drivers; - Memory management; - Multiple devices driver; - ARM64 architecture; - EROFS file system; - Networking core; - eXpress Data Path; - ARM32 architecture; - M68K architecture; - MIPS architecture; - OpenRISC architecture; - PA-RISC architecture; - PowerPC architecture; - RISC-V architecture; - S390 architecture; - User-Mode Linux (UML); - x86 architecture; - Block layer subsystem; - Cryptographic API; - Compute Acceleration Framework; - Intel NPU Driver; - Speakup Console Speech Driver; - ACPI drivers; - Serial ATA and Parallel ATA drivers; - Auxiliary display drivers; - Drivers core; - Micron PCIe SSD driver; - Null block device driver; - Ublk userspace block driver; - Compressed RAM block device driver; - Bluetooth drivers; - Bus devices; - AMD CDX bus driver; - Hardware random number generator core; - Character device driver; - TPM device driver; - Clock framework and drivers; - Clocksource drivers; - CPU frequency scaling framework; - CPU idle management framework; - Hardware crypto device drivers; - CXL (Compute Express Link) drivers; - DAX dirext access to differentiated memory framework; - DIBS (Direct Internal Buffer Sharing) drivers; - Buffer Sharing and Synchronization framework;…

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CVE-2026-98550 — tipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow

USN-8959-1 — linux, linux-aws, linux-gcp, linux-hwe-7.0, linux-ibm, linux-oracle vulnerabilities