CVE-2025-39844 [中] | Security Vulnerability（Linux Kernel）

In the Linux kernel, the following vulnerability has been resolved: mm: move page table sync declarations to linux/pgtable.h During our internal testing, we started observing intermittent boot failures when the machine uses 4-level paging and has a large amount of persistent memory: BUG: unable to handle page fault for address: ffffe70000000034 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP NOPTI RIP: 0010:__init_single_page+0x9/0x6d Call Trace: <TASK> __init_zone_device_page+0x17/0x5d memmap_init_zone_device+0x154/0x1bb pagemap_range+0x2e0/0x40f memremap_pages+0x10b/0x2f0 devm_memremap_pages+0x1e/0x60 dev_dax_probe+0xce/0x2ec [device_dax] dax_bus_probe+0x6d/0xc9 [... snip ...] </TASK> It turns out that the kernel panics while initializing vmemmap (struct page array) when the vmemmap region spans two PGD entries, because the new PGD entry is only installed in init_mm.pgd, but not in the page tables of other tasks. And looking at __populate_section_memmap(): if (vmemmap_can_optimize(altmap, pgmap)) // does not sync top level page tables r = vmemmap_populate_compound_pages(pfn, start, end, nid, pgmap); else // sync top level page tables in x86 r = vmemmap_populate(start, end, nid, altmap); In the normal path, vmemmap_populate() in arch/x86/mm/init_64.c synchronizes the top level page table (See commit 9b861528a801 ("x86-64, mem: Update all PGDs for direct mapping and vmemmap mapping changes")) so that all tasks in the system can see the new vmemmap area. However, when vmemmap_can_optimize() returns true, the optimized path skips synchronization of top-level page tables. This is because vmemmap_populate_compound_pages() is implemented in core MM code, which does not handle synchronization of the top-level page tables. Instead, the core MM has historically relied on each architecture to perform this synchronization manually. We're not the first party to encounter a crash caused by not-sync'd top level page tables: earlier this year, Gwan-gyeong Mun attempted to address the issue [1] [2] after hitting a kernel panic when x86 code accessed the vmemmap area before the corresponding top-level entries were synced. At that time, the issue was believed to be triggered only when struct page was enlarged for debugging purposes, and the patch did not get further updates. It turns out that current approach of relying on each arch to handle the page table sync manually is fragile because 1) it's easy to forget to sync the top level page table, and 2) it's also easy to overlook that the kernel should not access the vmemmap and direct mapping areas before the sync. # The solution: Make page table sync more code robust and harder to miss To address this, Dave Hansen suggested [3] [4] introducing {pgd,p4d}_populate_kernel() for updating kernel portion of the page tables and allow each architecture to explicitly perform synchronization when installing top-level entries. With this approach, we no longer need to worry about missing the sync step, reducing the risk of future regressions. The new interface reuses existing ARCH_PAGE_TABLE_SYNC_MASK, PGTBL_P*D_MODIFIED and arch_sync_kernel_mappings() facility used by vmalloc and ioremap to synchronize page tables. pgd_populate_kernel() looks like this: static inline void pgd_populate_kernel(unsigned long addr, pgd_t *pgd, p4d_t *p4d) { pgd_populate(&init_mm, pgd, p4d); if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_PGD_MODIFIED) arch_sync_kernel_mappings(addr, addr); } It is worth noting that vmalloc() and apply_to_range() carefully synchronizes page tables by calling p*d_alloc_track() and arch_sync_kernel_mappings(), and thus they are not affected by ---truncated---

#	日付	旧 EPSS スコア	新 EPSS スコア	Δ（新 − 旧）
1	2026-06-15	0.02%	0.14%	+0.11%
2	2025-09-20	—	0.02%	—

日付

旧 EPSS スコア

新 EPSS スコア

Δ（新 − 旧）

2026-06-15

0.02%

0.14%

+0.11%

2025-09-20

—

0.02%

—

ベーススコア	バージョン	深刻度	ベクトル	悪用しやすさ	影響	スコアの出典
5.5	3.1	MEDIUM	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H` クリックして展開攻撃ベクター (AV:L) 対象ホスト上でコードを実行できること、または別ユーザーの誤操作・悪意ある操作が前提になる。攻撃の複雑さ (AC:L) 攻撃者が条件を満たせば、レース条件や珍しい構成に依存せずに再現しやすい。必要な権限 (PR:L) 一般ユーザー権限があれば足り、管理者（root 相当）は不要。ユーザーの関与 (UI:N) メールのリンクを開く、マクロを有効にするなど、被害者の協力がなくても成立しうる。スコープ (S:U) 影響は脆弱コンポーネントと同一のセキュリティ権限・信頼境界の内側に収まる。機密性への影響 (C:N) 機微情報の漏えいは想定しにくい。完全性への影響 (I:N) 改ざん・なりすましによる信頼毀損は軽微か、想定されない。可用性への影響 (A:H) 長時間のサービス停止、データ損壊による復旧不能に近い状態など、利用者に著しい不便を与えうる。	1.8	3.6	[email protected]

ベーススコア

バージョン

深刻度

ベクトル

悪用しやすさ

影響

スコアの出典

5.5

3.1

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H クリックして展開

攻撃ベクター (AV:L): 対象ホスト上でコードを実行できること、または別ユーザーの誤操作・悪意ある操作が前提になる。
攻撃の複雑さ (AC:L): 攻撃者が条件を満たせば、レース条件や珍しい構成に依存せずに再現しやすい。
必要な権限 (PR:L): 一般ユーザー権限があれば足り、管理者（root 相当）は不要。
ユーザーの関与 (UI:N): メールのリンクを開く、マクロを有効にするなど、被害者の協力がなくても成立しうる。
スコープ (S:U): 影響は脆弱コンポーネントと同一のセキュリティ権限・信頼境界の内側に収まる。
機密性への影響 (C:N): 機微情報の漏えいは想定しにくい。
完全性への影響 (I:N): 改ざん・なりすましによる信頼毀損は軽微か、想定されない。
可用性への影響 (A:H): 長時間のサービス停止、データ損壊による復旧不能に近い状態など、利用者に著しい不便を与えうる。

1.8

3.6

[email protected]

CVE-2025-39844 の OS トラッカー

vendor	priority	summary	link
`debian`	unimportant	CVE-2025-39844 unimportant priority: Debian including 2 source packages (linux, linux-6.1), 6 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 6.	https://security-tracker.debian.org/tracker/CVE-2025-39844
`redhat`	—	—	https://access.redhat.com/security/cve/CVE-2025-39844
`suse`	medium	CVE-2025-39844 severity moderate: SUSE including 466 source package names (2.1.3-6.80:kernel-default-base-6.4.0-35.1.21.12, 2.1.3-7.57:kernel-default-6.4.0-35.1, …), 972 product×package rows across 197 product lines (Container suse/sl-micro/6.0/base-os-container, Container suse/sl-micro/6.0/kvm-os-container, … (197 product lines)): Fixed 619, Known Affected 231, Known Not Affected 101, First Fixed 21.	https://www.suse.com/security/cve/CVE-2025-39844/
`ubuntu`	medium	CVE-2025-39844 medium priority: Ubuntu including 158 source packages (linux, linux-allwinner-5.19, …), 1414 status rows across 9 suites (bionic, focal, jammy, noble, plucky, questing, trusty, upstream, xenial): DNE 1017, ignored 176, released 149, not-affected 62, needed 6, needs-triage 2, pending 2.	https://ubuntu.com/security/CVE-2025-39844

CVE-2025-39844 の影響を受けるソフトウェア／構成

ベンダー	製品	バージョン	生の CPE
linux	linux_kernel	>= 5.13, < 5.15.192	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 5.16, < 6.1.151	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.2, < 6.6.105	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.7, < 6.12.46	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.13, < 6.16.6	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	6.17	cpe:2.3:o:linux:linux_kernel:6.17:rc1::::::
linux	linux_kernel	6.17	cpe:2.3:o:linux:linux_kernel:6.17:rc2::::::
linux	linux_kernel	6.17	cpe:2.3:o:linux:linux_kernel:6.17:rc3::::::
linux	linux_kernel	6.17	cpe:2.3:o:linux:linux_kernel:6.17:rc4::::::
debian	debian_linux	11.0	cpe:2.3:o:debian:debian_linux:11.0:::::::*

CVE-2025-39844 の参考情報

URL	タグ
https://git.kernel.org/stable/c/469f9d22751472b81eaaf8a27fcdb5a70741c342	Patch
https://git.kernel.org/stable/c/4f7537772011fad832f83d6848f8eab282545bef	Patch
https://git.kernel.org/stable/c/6797a8b3f71b2cb558b8771a03450dc3e004e453	Patch
https://git.kernel.org/stable/c/732e62212f49d549c91071b4da7942ee3058f7a2	Patch
https://git.kernel.org/stable/c/7cc183f2e67d19b03ee5c13a6664b8c6cc37ff9d	Patch
https://git.kernel.org/stable/c/eceb44e1f94bd641b2a4e8c09b64c797c4eabc15	Patch
https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html	Mailing List Third Party Advisory
https://cert-portal.siemens.com/productcert/html/ssa-032379.html

URL

タグ

https://git.kernel.org/stable/c/469f9d22751472b81eaaf8a27fcdb5a70741c342

Patch

https://git.kernel.org/stable/c/4f7537772011fad832f83d6848f8eab282545bef

Patch

https://git.kernel.org/stable/c/6797a8b3f71b2cb558b8771a03450dc3e004e453

Patch

https://git.kernel.org/stable/c/732e62212f49d549c91071b4da7942ee3058f7a2

Patch

https://git.kernel.org/stable/c/7cc183f2e67d19b03ee5c13a6664b8c6cc37ff9d

Patch