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CVE-2026-43418— sched/mmcid: Prevent CID stalls due to concurrent forks

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.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于sched/mmcid模块在fork()过程中新任务尚未可见时即分配CID，导致并发fork引发CID分配失败。

AI Predicted 5.5 Difficulty: Trivial EPSS 0.14% · P3

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 6

VendorProduct Version RangeStatus
Linux Linux fbd0e71dc370af73f6b316e4de9eed273dd90340< f0189d49282e0458f3a737bd486c1ec048148f66 affected
fbd0e71dc370af73f6b316e4de9eed273dd90340< b2e48c429ec54715d16fefa719dd2fbded2e65be affected
6.19 affected
< 6.19 unaffected
6.19.9≤ 6.19.* unaffected
7.0≤ * unaffected
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I. Basic Information for CVE-2026-43418

Vulnerability Information
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Vulnerability Title
sched/mmcid: Prevent CID stalls due to concurrent forks
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: sched/mmcid: Prevent CID stalls due to concurrent forks A newly forked task is accounted as MMCID user before the task is visible in the process' thread list and the global task list. This creates the following problem: CPU1 CPU2 fork() sched_mm_cid_fork(tnew1) tnew1->mm.mm_cid_users++; tnew1->mm_cid.cid = getcid() -> preemption fork() sched_mm_cid_fork(tnew2) tnew2->mm.mm_cid_users++; // Reaches the per CPU threshold mm_cid_fixup_tasks_to_cpus() for_each_other(current, p) .... As tnew1 is not visible yet, this fails to fix up the already allocated CID of tnew1. As a consequence a subsequent schedule in might fail to acquire a (transitional) CID and the machine stalls. Move the invocation of sched_mm_cid_fork() after the new task becomes visible in the thread and the task list to prevent this. This also makes it symmetrical vs. exit() where the task is removed as CID user before the task is removed from the thread and task lists.
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
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于sched/mmcid模块在fork()过程中新任务尚未可见时即分配CID，导致并发fork引发CID分配失败。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux fbd0e71dc370af73f6b316e4de9eed273dd90340 ~ f0189d49282e0458f3a737bd486c1ec048148f66 -
Linux Linux 6.19 -

II. Public POCs for CVE-2026-43418

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III. Intelligence Information for CVE-2026-43418

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Patches & Fixes for CVE-2026-43418 (2)

Same Patch Batch · Linux · 2026-05-08 · 197 CVEs total

CVE-2026-43384 9.8 CRITICAL net/tcp-ao: Fix MAC comparison to be constant-time
CVE-2026-43341 9.8 CRITICAL net/ipv6: ioam6: prevent schema length wraparound in trace fill
CVE-2026-43304 9.8 CRITICAL libceph: define and enforce CEPH_MAX_KEY_LEN
CVE-2026-43379 9.8 CRITICAL ksmbd: fix use-after-free in smb_lazy_parent_lease_break_close()
CVE-2026-43378 9.8 CRITICAL smb: server: fix use-after-free in smb2_open()
CVE-2026-43465 9.8 CRITICAL net/mlx5e: RX, Fix XDP multi-buf frag counting for striding RQ
CVE-2026-43414 9.8 CRITICAL scsi: qla2xxx: Completely fix fcport double free
CVE-2026-43376 9.8 CRITICAL ksmbd: fix use-after-free by using call_rcu() for oplock_info
CVE-2026-43402 9.8 CRITICAL kthread: consolidate kthread exit paths to prevent use-after-free
CVE-2026-43383 9.4 CRITICAL net/tcp-md5: Fix MAC comparison to be constant-time
CVE-2026-43407 9.1 CRITICAL libceph: Fix potential out-of-bounds access in ceph_handle_auth_reply()
CVE-2026-43406 9.1 CRITICAL libceph: prevent potential out-of-bounds reads in process_message_header()
CVE-2026-43284 8.8 HIGH xfrm: esp: avoid in-place decrypt on shared skb frags
CVE-2026-43334 8.8 HIGH Bluetooth: SMP: force responder MITM requirements before building the pairing response
CVE-2026-43322 8.8 HIGH Bluetooth: hci_sync: Fix UAF in le_read_features_complete
CVE-2026-43403 8.8 HIGH nsfs: tighten permission checks for ns iteration ioctls
CVE-2026-43391 8.8 HIGH nsfs: tighten permission checks for handle opening
CVE-2026-43291 8.3 HIGH net: nfc: nci: Fix parameter validation for packet data
CVE-2026-43466 8.2 HIGH net/mlx5e: Fix DMA FIFO desync on error CQE SQ recovery
CVE-2026-43365 8.2 HIGH xfs: fix undersized l_iclog_roundoff values

Showing top 20 of 197 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-43418

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