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

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Linux 内核中，以下漏洞已被修复： tipc：拒绝无效和意外的 GRP_ACK_MSG，以防止 bc_ackers 下溢 提交 48a5fe38772b（"tipc: 修复因重复 GRP_ACK_MSG 导致的 bc_ackers 下溢”）通过在 中，当满足 条件时提前返回，从而拒绝处理重复或过期的 ACK 消息。 然而，该检查仍存在两个方面的不足： 1. 当 为零时（例如在静默组中、未请求 replicast ACK，或所有预期成员均已确认之后），若收到一个意外的 且其 ，该消息会通过 检查，并无条件地递

AI Predicted 5.9 Difficulty: Hard

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux 2f487712b89376fce267223bbb0db93d393d4b09< edc6593c442278fceff0120e8cc58bc592168c35 affected
2f487712b89376fce267223bbb0db93d393d4b09< 9b94a90651e1fa573c6ac6a5a6b269d5874df2c0 affected
2f487712b89376fce267223bbb0db93d393d4b09< 507a27435b2bb1f22e3a3674f6a6553eb815021b affected
2f487712b89376fce267223bbb0db93d393d4b09< 80a9ccfc24d3776ef6753a57315e726475fac7d7 affected
2f487712b89376fce267223bbb0db93d393d4b09< 478fb08d0c2a53002a721d22b8d6681ec971d90f affected
2f487712b89376fce267223bbb0db93d393d4b09< 12cc3a1eac5a2a06b67a7b85f0f48ff241a94d1b affected
2f487712b89376fce267223bbb0db93d393d4b09< b0e517961f09b9f60d338d1ea4e17aacdbf206f0 affected
2f487712b89376fce267223bbb0db93d393d4b09< 99cc2a62e07a44a22254d7beca9ef1f8ad886d0d affected
… +10 more rows
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I. Basic Information for CVE-2026-98550

Vulnerability Information
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Vulnerability Title
tipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow
Source: CVE Program / CVE List V5
Vulnerability Description
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 value (such as S) is received. A member sending acked = S followed by acked = S + 1 could decrement grp->bc_ackers twice in the same round, prematurely clearing bc_ackers or underflowing it. Fix this by: - Dropping GRP_ACK_MSG immediately if grp->bc_ackers is zero. - Requiring acked == grp->bc_snd_nxt and rejecting duplicates where m->bc_acked == acked. Because replicast broadcast rounds are strictly sequential, only grp->bc_snd_nxt can be acknowledged, and each member can acknowledge at most once per round. Note that a related pre-existing issue in tipc_group_delete_member() (where grp->bc_ackers decrementing to zero upon member departure does not restore *grp->open or trigger a socket wakeup) will be addressed in a separate patch.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 2f487712b89376fce267223bbb0db93d393d4b09 ~ edc6593c442278fceff0120e8cc58bc592168c35 -
Linux Linux 4.15 -

II. Public POCs for CVE-2026-98550

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III. Intelligence Information for CVE-2026-98550

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Patches & Fixes for CVE-2026-98550 (8)

Same Patch Batch · Linux · 2026-10-18 · 436 CVEs total

CVE-2026-98583 nfc: nfcmrvl: validate helper command length before pull
CVE-2026-98570 net: ipv6: keep room for the mac header in dst_dev_overhead()
CVE-2026-98571 net: stmmac: clear stale buf->page after recycling on skb build failure
CVE-2026-98572 bpf: Fix immediate JMP JEQ/JNE on MIPS32
CVE-2026-98573 net: skbuff: fix pull-bound underflow in skb_checksum_setup_ipv6()
CVE-2026-98574 net: bcmgenet: stop Tx NAPI before disabling the queues
CVE-2026-98575 nfc: pn533: fix OOB read in pn533_acr122_is_rx_frame_valid()
CVE-2026-98576 nfc: llcp: fix slab-out-of-bounds reads when logging service names
CVE-2026-98577 nfc: llcp: fix WKS SAP hijacking via prefix match in nfc_llcp_wks_sap()
CVE-2026-98578 nfc: st21nfca: validate ISO15693 inventory length
CVE-2026-98579 nfc: llcp: fix sdreq TLV list leak on parse/alloc/send failure
CVE-2026-98580 nfc: llcp: Fix race condition in accept_queue lifecycle
CVE-2026-98581 nfc: llcp: Fix list corruption / refcount desync in nfc_llcp_recv_dm()
CVE-2026-98582 nfc: st21nfca: validate received frame size
CVE-2026-98594 tg3: clean up PHYLIB resources on probe failure
CVE-2026-98591 bpf: Fix bounds check for skb-backed dynptrs
CVE-2026-98592 net: spacemit: clear TX descriptor on fragment mapping failure
CVE-2026-98593 s390/debug: Fix NULL pointer dereference in debug_info_copy()
CVE-2026-98590 bpf: Fix bpf_sock context code generation
CVE-2026-98595 udp: remove a disconnected socket from the 4-tuple hash table

Showing top 20 of 436 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-98550

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