CVE-2025-21796: nfsd: clear acl_access/acl_default after releasing them

Critical severity · published Feb 27, 2025

CVE-2025-21796

nfsd: clear acl_access/acl_default after releasing them

9.8

CVSS

0.7%

EPSS

On KEV

Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: clear acl_access/acl_default after releasing them If getting acl_default fails, acl_access and acl_default will be released simultaneously. However, acl_access will still retain a pointer pointing to the released posix_acl, which will trigger a WARNING in nfs3svc_release_getacl like this: ------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 26 PID: 3199 at lib/refcount.c:28 refcount_warn_saturate+0xb5/0x170 Modules linked in: CPU: 26 UID: 0 PID: 3199 Comm: nfsd Not tainted 6.12.0-rc6-00079-g04ae226af01f-dirty #8 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014 RIP: 0010:refcount_warn_saturate+0xb5/0x170 Code: cc cc 0f b6 1d b3 20 a5 03 80 fb 01 0f 87 65 48 d8 00 83 e3 01 75 e4 48 c7 c7 c0 3b 9b 85 c6 05 97 20 a5 03 01 e8 fb 3e 30 ff <0f> 0b eb cd 0f b6 1d 8a3 RSP: 0018:ffffc90008637cd8 EFLAGS: 00010282 RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff83904fde RDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88871ed36380 RBP: ffff888158beeb40 R08: 0000000000000001 R09: fffff520010c6f56 R10: ffffc90008637ab7 R11: 0000000000000001 R12: 0000000000000001 R13: ffff888140e77400 R14: ffff888140e77408 R15: ffffffff858b42c0 FS: 0000000000000000(0000) GS:ffff88871ed00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000562384d32158 CR3: 000000055cc6a000 CR4: 00000000000006f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> ? refcount_warn_saturate+0xb5/0x170 ? __warn+0xa5/0x140 ? refcount_warn_saturate+0xb5/0x170 ? report_bug+0x1b1/0x1e0 ? handle_bug+0x53/0xa0 ? exc_invalid_op+0x17/0x40 ? asm_exc_invalid_op+0x1a/0x20 ? tick_nohz_tick_stopped+0x1e/0x40 ? refcount_warn_saturate+0xb5/0x170 ? refcount_warn_saturate+0xb5/0x170 nfs3svc_release_getacl+0xc9/0xe0 svc_process_common+0x5db/0xb60 ? __pfx_svc_process_common+0x10/0x10 ? __rcu_read_unlock+0x69/0xa0 ? __pfx_nfsd_dispatch+0x10/0x10 ? svc_xprt_received+0xa1/0x120 ? xdr_init_decode+0x11d/0x190 svc_process+0x2a7/0x330 svc_handle_xprt+0x69d/0x940 svc_recv+0x180/0x2d0 nfsd+0x168/0x200 ? __pfx_nfsd+0x10/0x10 kthread+0x1a2/0x1e0 ? kthread+0xf4/0x1e0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x34/0x60 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK> Kernel panic - not syncing: kernel: panic_on_warn set ... Clear acl_access/acl_default after posix_acl_release is called to prevent UAF from being triggered.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack vector

Network

Complexity

Low

Privileges

None

User interaction

None

Confidentiality

High

Integrity

High

Availability

High

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.7% · higher than 52% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

Kernel · Linux

2.6.13 before 5.10.235; 5.11 before 5.15.179; 5.16 before 6.1.129; 6.2 before 6.6.79; 6.7 before 6.12.16; 6.13 before 6.13.4; +2 more · source: NVD

Linux · Linux

a257cdd0e2179630d3201c32ba14d7fcb3c3a055 before 8a1737ae42c928384ab6447f6ee1a882510e85fa; a257cdd0e2179630d3201c32ba14d7fcb3c3a055 before 6f7cfee1a316891890c505563aa54f3476db52fd; a257cdd0e2179630d3201c32ba14d7fcb3c3a055 before 2e59b2b68782519560b3d6a41dd66a3d01a01cd3; a257cdd0e2179630d3201c32ba14d7fcb3c3a055 before 55d947315fb5f67a35e4e1d3e01bb886b9c6decf; a257cdd0e2179630d3201c32ba14d7fcb3c3a055 before f8d871523142f7895f250a856f8c4a4181614510; a257cdd0e2179630d3201c32ba14d7fcb3c3a055 before 1fd94884174bd20beb1773990fd3b1aa877688d9; +2 more · source: vendor

SIMATIC S7-1500 CPU 1518-4 PN/DP MFP · Siemens

V3.1.5; V3.1.6; V3.1.7; V3.1.5; V3.1.6; V3.1.7 · source: CISA

SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP · Siemens

V3.1.5; V3.1.6; V3.1.7; V3.1.5; V3.1.6; V3.1.7 · source: CISA

SIMATIC S7-1500 TM MFP - GNU/Linux subsystem · Siemens

0; 0 · source: CISA

SIPLUS S7-1500 CPU 1518-4 PN/DP MFP · Siemens

V3.1.5; V3.1.6; V3.1.7 · source: CISA

In the news

VulnerabilityHigh

Siemens SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP

View CSAF Summary Multiple vulnerabilities have been identified in the additional GNU/Linux subsystem of the firmware version V3.1.6 for the SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP (incl. SIPLUS variant). Siemens is preparing fix versions and recommends specific countermeasures for products where fixes are not, or not yet available. The following versions of Siemens SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP are affected: SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) vers:intdot/>=3.1.6 (CVE-2021-41617, CVE-2023-28531, CVE-2023-51384, CVE-2023-52927, CVE-2024-26783, CVE-2024-27056, CVE-2024-28956, CVE-2024-36903, CVE-2024-36927, CVE-2024-42079, CVE-2024-46786, CVE-2024-47736, CVE-2024-47809, CVE-2024-49968, CVE-2024-49994, CVE-2024-49998, CVE-2024-50014, CVE-2024-50063, CVE-2024-50164, CVE-2024-50298, CVE-2024-53124, CVE-2024-53170, CVE-2024-54458, CVE-2024-56631, CVE-2024-56703, CVE-2024-56719, CVE-2024-57917, CVE-2024-57924, CVE-2024-57973, CVE-2024-57977, CVE-2024-57979, CVE-2024-58011, CVE-2024-58016, CVE-2024-58020, CVE-2024-58056, CVE-2024-58058, CVE-2024-58061, CVE-2024-58086, CVE-2025-21645, CVE-2025-21648, CVE-2025-21655, CVE-2025-21676, CVE-2025-21682, CVE-2025-21702, CVE-2025-21705, CVE-2025-21706, CVE-2025-21707, CVE-2025-21718, CVE-2025-21731, CVE-2025-21745, CVE-2025-21758, CVE-2025-21760, CVE-2025-21764, CVE-2025-21765, CVE-2025-21780, CVE-2025-21795, CVE-2025-21796, CVE-2025-21802, CVE-2025-21814, CVE-2025-21846, CVE-2025-21853, CVE-2...

CVE-2021-41617 CVE-2023-28531 CVE-2023-51384

Jul 28, 2026·CISA Advisories

Affected product

Kernel

Linux

All Kernel CVEs

References

NVD

https://nvd.nist.gov/vuln/detail/CVE-2025-21796

CVE.org

https://www.cve.org/CVERecord?id=CVE-2025-21796

Patch