9.8

CVE-2025-21796: linux Use After Free

CVSS: 9.8v3.1CriticalModified
AliasesUBUNTU-CVE-2025-21796DEBIAN-CVE-2025-21796
Published 27-02-2025Last modified 15-10-2026
Open JSON

Vulnerability summary

CVE-2025-21796 is a critical (CVSS 9.8) Use After Free vulnerability in linux. EPSS estimates a 0.67% chance of exploitation in the next 30 days, higher than 51.2% of scored vulnerabilities.

Overall risk
70/100
0100
High · default modelHow is this calculated?
CVSS score
9.8/10
010
Critical · v3.1 (CVE.org)
EPSS score
0.67%
0%100%
Low · +0.04 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 55 · Related 51
DLA-4102-1DLA-4178-1RHSA-2025:20095RHSA-2025:20518SUSE-SU-2025:01919-1SUSE-SU-2025:01951-1

Timeline

  1. 27-02-2025
    PublishedVulnerability first disclosed.
  2. 15-10-2026
    Last modifiedVulnerability information updated.

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 metrics

4 scores · 4 sources · 1 version

EPSS trend

Probability

0.67%

Chance of exploitation in the next 30 days

Percentile

51%

Versus all other CVEs

30-day change

+0.04 pp

From 0.64% on 19-09-2026

19-09-202619-10-2026
EPSS score
0.67%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Ubuntu137 products
  • linuxAll versions (No fix recorded) | < 4.4.0-273.307 | < 4.15.0-242.254 | < 5.4.0-222.242 | < 5.15.0-140.150 | < 6.8.0-78.78
  • linux-allwinner-5.19All versions (No fix recorded)
  • linux-aws< 4.4.0-1148.154 | < 4.4.0-1186.201 | < 4.15.0-1185.198 | < 5.4.0-1151.161 | < 5.15.0-1084.91 | < 6.8.0-1035.37
  • linux-aws-5.0All versions (No fix recorded)
  • linux-aws-5.11All versions (No fix recorded)
Linux2 products
  • linux≥ a257cdd0e2179630d3201c32ba14d7fcb3c3a055, < 8a1737ae42c928384ab6447f6ee1a882510e85fa | ≥ a257cdd0e2179630d3201c32ba14d7fcb3c3a055, < 6f7cfee1a316891890c505563aa54f3476db52fd | ≥ a257cdd0e2179630d3201c32ba14d7fcb3c3a055, < 2e59b2b68782519560b3d6a41dd66a3d01a01cd3 | ≥ a257cdd0e2179630d3201c32ba14d7fcb3c3a055, < 55d947315fb5f67a35e4e1d3e01bb886b9c6decf | ≥ a257cdd0e2179630d3201c32ba14d7fcb3c3a055, < f8d871523142f7895f250a856f8c4a4181614510 | ≥ a257cdd0e2179630d3201c32ba14d7fcb3c3a055, < 1fd94884174bd20beb1773990fd3b1aa877688d9 | ≥ a257cdd0e2179630d3201c32ba14d7fcb3c3a055, < 7faf14a7b0366f153284db0ad3347c457ea70136 | 2.6.13
  • linux_kernel≥ 2.6.13, < 5.10.235 | ≥ 5.11, < 5.15.179 | ≥ 5.16, < 6.1.129 | ≥ 6.2, < 6.6.79 | ≥ 6.7, < 6.12.16 | ≥ 6.13, < 6.13.4 | 6.14:rc1 | 6.14:rc2
Debian1 product
  • linux< 6.1.129-1 | < 6.12.16-1

3 vendors · 140 products

References

59 links
Show all 59 references