UBUNTU-CVE-2025-21796: Use After Free

Q: Which deployments should be prioritized for investigation?

Prioritize Ubuntu systems using the listed Linux kernel packages where the NFS server daemon, nfsd, is running. The reported failure occurs in the NFSv3 ACL handling and release path, specifically nfs3svc_release_getacl.

Q: What condition leads to the use-after-free warning?

The issue is triggered when obtaining acl_default fails after acl_access and acl_default are released together. The acl_access pointer is not cleared and can still reference the released POSIX ACL.

Q: How can administrators identify a potentially affected runtime event?

Check kernel logs for a refcount underflow or use-after-free warning associated with nfsd, particularly a stack trace naming nfs3svc_release_getacl. The reported warning originates from refcount_warn_saturate in lib/refcount.c.

Published Feb 27, 2025

Updated

In the Linux kernel, the following vulnerability has been resolved: nfsd: clear aclaccess/acldefault after releasing them If getting acldefault fails, aclaccess and acldefault will be released simultaneously. However, aclaccess will still retain a pointer pointing to the released posixacl, which will trigger a WARNING in nfs3svcreleasegetacl like this: ------------[ cut here ]------------ refcountt: underflow; use-after-free. WARNING: CPU: 26 PID: 3199 at lib/refcount.c:28 refcountwarnsaturate+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:refcountwarnsaturate+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> ? refcountwarnsaturate+0xb5/0x170 ? warn+0xa5/0x140 ? refcountwarnsaturate+0xb5/0x170 ? reportbug+0x1b1/0x1e0 ? handlebug+0x53/0xa0 ? excinvalidop+0x17/0x40 ? asmexcinvalidop+0x1a/0x20 ? ticknohztickstopped+0x1e/0x40 ? refcountwarnsaturate+0xb5/0x170 ? refcountwarnsaturate+0xb5/0x170 nfs3svcreleasegetacl+0xc9/0xe0 svcprocesscommon+0x5db/0xb60 ? pfxsvcprocesscommon+0x10/0x10 ? rcureadunlock+0x69/0xa0 ? pfxnfsddispatch+0x10/0x10 ? svcxprtreceived+0xa1/0x120 ? xdrinitdecode+0x11d/0x190 svcprocess+0x2a7/0x330 svchandlexprt+0x69d/0x940 svcrecv+0x180/0x2d0 nfsd+0x168/0x200 ? pfxnfsd+0x10/0x10 kthread+0x1a2/0x1e0 ? kthread+0xf4/0x1e0 ? pfxkthread+0x10/0x10 retfromfork+0x34/0x60 ? pfxkthread+0x10/0x10 retfromforkasm+0x1a/0x30 </TASK> Kernel panic - not syncing: kernel: paniconwarn set ... Clear aclaccess/acldefault after posixaclrelease is called to prevent UAF from being triggered.

Affected Software

209 affected componentsFixes available

ubuntu/linux*

ubuntu/linux-aws<4.4.0-1148.154

4.4.0-1148.154

ubuntu/linux-azure<4.15.0-1193.208~14.04.1

4.15.0-1193.208~14.04.1

ubuntu/linux-lts-xenial<4.4.0-273.307~14.04.1

4.4.0-273.307~14.04.1

ubuntu/linux<4.4.0-273.307

4.4.0-273.307

ubuntu/linux-aws<4.4.0-1186.201

4.4.0-1186.201

ubuntu/linux-aws-hwe<4.15.0-1185.198~16.04.1

4.15.0-1185.198~16.04.1

ubuntu/linux-azure<4.15.0-1193.208~16.04.1

4.15.0-1193.208~16.04.1

ubuntu/linux-gcp<4.15.0-1178.195~16.04.1

4.15.0-1178.195~16.04.1

ubuntu/linux-hwe<4.15.0-242.254~16.04.1

4.15.0-242.254~16.04.1

ubuntu/linux-kvm<4.4.0-1149.160

4.4.0-1149.160

ubuntu/linux-oracle<4.15.0-1148.159~16.04.1

4.15.0-1148.159~16.04.1

ubuntu/linux-hwe-edge*

ubuntu/linux-fips<4.4.0-1119.126

4.4.0-1119.126

ubuntu/linux-fips*

ubuntu/linux<4.15.0-242.254

4.15.0-242.254

ubuntu/linux-aws<4.15.0-1185.198

4.15.0-1185.198

ubuntu/linux-aws-5.0*

ubuntu/linux-aws-5.3*

ubuntu/linux-aws-5.4<5.4.0-1151.161~18.04.1

5.4.0-1151.161~18.04.1

ubuntu/linux-azure*

ubuntu/linux-azure-4.15<4.15.0-1193.208

4.15.0-1193.208

ubuntu/linux-azure-5.3*

ubuntu/linux-azure-5.4<5.4.0-1154.161~18.04.1

5.4.0-1154.161~18.04.1

ubuntu/linux-azure-edge*

ubuntu/linux-gcp*

ubuntu/linux-gcp-4.15<4.15.0-1178.195

4.15.0-1178.195

ubuntu/linux-gcp-5.3*

ubuntu/linux-gcp-5.4<5.4.0-1154.163~18.04.1

5.4.0-1154.163~18.04.1

ubuntu/linux-gke-4.15*

ubuntu/linux-gke-5.4*

ubuntu/linux-gkeop-5.4*

ubuntu/linux-hwe*

ubuntu/linux-hwe-5.4<5.4.0-222.242~18.04.1

5.4.0-222.242~18.04.1

ubuntu/linux-hwe-edge*

ubuntu/linux-ibm-5.4<5.4.0-1097.102~18.04.1

5.4.0-1097.102~18.04.1

ubuntu/linux-kvm<4.15.0-1168.173

4.15.0-1168.173

ubuntu/linux-oem*

ubuntu/linux-oracle<4.15.0-1147.158

4.15.0-1147.158

ubuntu/linux-oracle-5.0*

ubuntu/linux-oracle-5.3*

ubuntu/linux-oracle-5.4<5.4.0-1149.159~18.04.1

5.4.0-1149.159~18.04.1

ubuntu/linux-raspi-5.4<5.4.0-1134.147~18.04.1

5.4.0-1134.147~18.04.1

ubuntu/linux-aws-fips<4.15.0-2123.129

4.15.0-2123.129

ubuntu/linux-azure-fips<4.15.0-2102.108

4.15.0-2102.108

ubuntu/linux-fips<4.15.0-1140.151

4.15.0-1140.151

ubuntu/linux-gcp-fips<4.15.0-2086.92

4.15.0-2086.92

ubuntu/linux-aws-fips*

ubuntu/linux-azure-fips*

ubuntu/linux-fips*

ubuntu/linux-gcp-fips*

ubuntu/linux-aws-5.15<5.15.0-1084.91~20.04.1

5.15.0-1084.91~20.04.1

ubuntu/linux-azure-5.15<5.15.0-1089.98~20.04.1

5.15.0-1089.98~20.04.1

ubuntu/linux-gcp-5.15<5.15.0-1083.92~20.04.1

5.15.0-1083.92~20.04.1

ubuntu/linux-ibm-5.15<5.15.0-1076.79~20.04.1

5.15.0-1076.79~20.04.1

ubuntu/linux-intel-iotg-5.15<5.15.0-1079.85~20.04.1

5.15.0-1079.85~20.04.1

ubuntu/linux-lowlatency-hwe-5.15<5.15.0-140.150~20.04.1

5.15.0-140.150~20.04.1

ubuntu/linux-oracle-5.15<5.15.0-1081.87~20.04.1

5.15.0-1081.87~20.04.1

ubuntu/linux-riscv-5.15<5.15.0-1079.83~20.04.1

5.15.0-1079.83~20.04.1

ubuntu/linux<5.4.0-222.242

5.4.0-222.242

ubuntu/linux-aws<5.4.0-1151.161

5.4.0-1151.161

ubuntu/linux-aws-5.11*

ubuntu/linux-aws-5.13*

ubuntu/linux-aws-5.8*

ubuntu/linux-azure<5.4.0-1154.161

5.4.0-1154.161

ubuntu/linux-azure-5.11*

ubuntu/linux-azure-5.13*

ubuntu/linux-azure-5.8*

ubuntu/linux-azure-fde*

ubuntu/linux-bluefield<5.4.0-1110.117

5.4.0-1110.117

ubuntu/linux-gcp<5.4.0-1154.163

5.4.0-1154.163

ubuntu/linux-gcp-5.11*

ubuntu/linux-gcp-5.13*

ubuntu/linux-gcp-5.8*

ubuntu/linux-gke*

ubuntu/linux-gke-5.15*

ubuntu/linux-gkeop*

ubuntu/linux-gkeop-5.15*

ubuntu/linux-hwe-5.11*

ubuntu/linux-hwe-5.13*

ubuntu/linux-hwe-5.15<5.15.0-142.152~20.04.1

5.15.0-142.152~20.04.1

ubuntu/linux-hwe-5.8*

ubuntu/linux-ibm<5.4.0-1097.102

5.4.0-1097.102

ubuntu/linux-intel-5.13*

ubuntu/linux-iot<5.4.0-1055.58

5.4.0-1055.58

ubuntu/linux-kvm<5.4.0-1138.147

5.4.0-1138.147

ubuntu/linux-nvidia-tegra-5.15<5.15.0-1039.39~20.04.1

5.15.0-1039.39~20.04.1

ubuntu/linux-oem-5.10*

ubuntu/linux-oem-5.13*

ubuntu/linux-oem-5.6*

ubuntu/linux-oracle<5.4.0-1149.159

5.4.0-1149.159

ubuntu/linux-oracle-5.11*

ubuntu/linux-oracle-5.13*

ubuntu/linux-oracle-5.8*

ubuntu/linux-raspi<5.4.0-1134.147

5.4.0-1134.147

ubuntu/linux-raspi2*

ubuntu/linux-riscv*

ubuntu/linux-riscv-5.11*

ubuntu/linux-riscv-5.8*

ubuntu/linux-xilinx-zynqmp<5.4.0-1069.73

5.4.0-1069.73

ubuntu/linux-aws-fips<5.4.0-1151.161+fips1

5.4.0-1151.161+fips1

ubuntu/linux-azure-fips<5.4.0-1155.162+fips1

5.4.0-1155.162+fips1

ubuntu/linux-fips<5.4.0-1125.135

5.4.0-1125.135

ubuntu/linux-gcp-fips<5.4.0-1154.163+fips1

5.4.0-1154.163+fips1

ubuntu/linux-aws-fips*

ubuntu/linux-azure-fips*

ubuntu/linux-fips*

ubuntu/linux-gcp-fips*

ubuntu/linux<5.15.0-140.150

5.15.0-140.150

ubuntu/linux-allwinner-5.19*

ubuntu/linux-aws<5.15.0-1084.91

5.15.0-1084.91

ubuntu/linux-aws-5.19*

ubuntu/linux-aws-6.2*

ubuntu/linux-aws-6.5*

ubuntu/linux-aws-6.8<6.8.0-1035.37~22.04.1

6.8.0-1035.37~22.04.1

ubuntu/linux-azure<5.15.0-1089.98

5.15.0-1089.98

ubuntu/linux-azure-5.19*

ubuntu/linux-azure-6.2*

ubuntu/linux-azure-6.5*

ubuntu/linux-azure-6.8<6.8.0-1034.39~22.04.1

6.8.0-1034.39~22.04.1

ubuntu/linux-azure-fde<5.15.0-1089.98.1

5.15.0-1089.98.1

ubuntu/linux-azure-fde-5.19*

ubuntu/linux-azure-fde-6.2*

ubuntu/linux-gcp<5.15.0-1083.92

5.15.0-1083.92

ubuntu/linux-gcp-5.19*

ubuntu/linux-gcp-6.2*

ubuntu/linux-gcp-6.5*

ubuntu/linux-gcp-6.8<6.8.0-1036.38~22.04.1

6.8.0-1036.38~22.04.1

ubuntu/linux-gke<5.15.0-1081.87

5.15.0-1081.87

ubuntu/linux-gkeop<5.15.0-1066.74

5.15.0-1066.74

ubuntu/linux-hwe-5.19*

ubuntu/linux-hwe-6.2*

ubuntu/linux-hwe-6.5*

ubuntu/linux-hwe-6.8<6.8.0-78.78~22.04.1

6.8.0-78.78~22.04.1

ubuntu/linux-ibm<5.15.0-1076.79

5.15.0-1076.79

ubuntu/linux-ibm-6.8<6.8.0-1033.33~22.04.1

6.8.0-1033.33~22.04.1

ubuntu/linux-intel-iot-realtime*

ubuntu/linux-intel-iotg<5.15.0-1079.85

5.15.0-1079.85

ubuntu/linux-kvm<5.15.0-1080.85

5.15.0-1080.85

ubuntu/linux-lowlatency<5.15.0-140.150

5.15.0-140.150

ubuntu/linux-lowlatency-hwe-5.19*

ubuntu/linux-lowlatency-hwe-6.2*

ubuntu/linux-lowlatency-hwe-6.5*

ubuntu/linux-lowlatency-hwe-6.8<6.8.0-78.78.1~22.04.1

6.8.0-78.78.1~22.04.1

ubuntu/linux-nvidia<5.15.0-1078.79

5.15.0-1078.79

ubuntu/linux-nvidia-6.2*

ubuntu/linux-nvidia-6.5*

ubuntu/linux-nvidia-6.8<6.8.0-1035.38~22.04.1

6.8.0-1035.38~22.04.1

ubuntu/linux-nvidia-tegra<5.15.0-1037.37

5.15.0-1037.37

ubuntu/linux-nvidia-tegra-igx<5.15.0-1026.26

5.15.0-1026.26

ubuntu/linux-oem-5.17*

ubuntu/linux-oem-6.0*

ubuntu/linux-oem-6.1*

ubuntu/linux-oem-6.5*

ubuntu/linux-oracle<5.15.0-1081.87

5.15.0-1081.87

ubuntu/linux-oracle-6.5*

ubuntu/linux-oracle-6.8<6.8.0-1032.33~22.04.1

6.8.0-1032.33~22.04.1

ubuntu/linux-raspi<5.15.0-1078.81

5.15.0-1078.81

ubuntu/linux-realtime*

ubuntu/linux-riscv*

ubuntu/linux-riscv-5.19*

ubuntu/linux-riscv-6.5*

ubuntu/linux-riscv-6.8<6.8.0-78.78~22.04.1

6.8.0-78.78~22.04.1

ubuntu/linux-starfive-5.19*

ubuntu/linux-starfive-6.2*

ubuntu/linux-starfive-6.5*

ubuntu/linux-xilinx-zynqmp<5.15.0-1050.54

5.15.0-1050.54

ubuntu/linux-bluefield<5.15.0-1066.68

5.15.0-1066.68

ubuntu/linux-intel-iot-realtime<5.15.0-1077.79

5.15.0-1077.79

ubuntu/linux-realtime<5.15.0-1084.93

5.15.0-1084.93

ubuntu/linux-realtime-6.8<6.8.1-1030.31~22.04.1

6.8.1-1030.31~22.04.1

ubuntu/linux-aws-fips*

ubuntu/linux-azure-fips*

ubuntu/linux-fips*

ubuntu/linux-gcp-fips*

ubuntu/linux-aws-fips<5.15.0-1084.91+fips1

5.15.0-1084.91+fips1

ubuntu/linux-azure-fips<5.15.0-1089.98+fips1

5.15.0-1089.98+fips1

ubuntu/linux-fips<5.15.0-140.150+fips1

5.15.0-140.150+fips1

ubuntu/linux-gcp-fips<5.15.0-1083.92+fips1

5.15.0-1083.92+fips1

ubuntu/linux<6.8.0-78.78

6.8.0-78.78

ubuntu/linux-aws<6.8.0-1035.37

6.8.0-1035.37

ubuntu/linux-azure<6.8.0-1034.39

6.8.0-1034.39

ubuntu/linux-azure-6.11<6.11.0-1015.15~24.04.1

6.11.0-1015.15~24.04.1

ubuntu/linux-azure-nvidia<6.8.0-1022.23

6.8.0-1022.23

ubuntu/linux-gcp<6.8.0-1036.38

6.8.0-1036.38

ubuntu/linux-gcp-6.11<6.11.0-1015.15~24.04.1

6.11.0-1015.15~24.04.1

ubuntu/linux-gke<6.8.0-1032.36

6.8.0-1032.36

ubuntu/linux-gkeop<6.8.0-1019.21

6.8.0-1019.21

ubuntu/linux-hwe-6.11<6.11.0-26.26~24.04.1

6.11.0-26.26~24.04.1

ubuntu/linux-ibm<6.8.0-1033.33

6.8.0-1033.33

ubuntu/linux-intel*

ubuntu/linux-lowlatency<6.8.0-78.78.1

6.8.0-78.78.1

ubuntu/linux-lowlatency-hwe-6.11<6.11.0-1014.15~24.04.1

6.11.0-1014.15~24.04.1

ubuntu/linux-nvidia<6.8.0-1035.38

6.8.0-1035.38

ubuntu/linux-nvidia-6.11<6.11.0-1010.10

6.11.0-1010.10

ubuntu/linux-nvidia-lowlatency<6.8.0-1035.38.1

6.8.0-1035.38.1

ubuntu/linux-nvidia-tegra<6.8.0-1009.9

6.8.0-1009.9

ubuntu/linux-oem-6.11<6.11.0-1022.22

6.11.0-1022.22

ubuntu/linux-oem-6.8*

ubuntu/linux-oracle<6.8.0-1032.33

6.8.0-1032.33

ubuntu/linux-raspi<6.8.0-1035.39

6.8.0-1035.39

ubuntu/linux-raspi-realtime*

ubuntu/linux-realtime*

ubuntu/linux-riscv*

ubuntu/linux-xilinx<6.8.0-1017.18

6.8.0-1017.18

ubuntu/linux-raspi-realtime<6.8.0-2028.29

6.8.0-2028.29

ubuntu/linux-realtime<6.8.1-1030.31

6.8.1-1030.31

ubuntu/linux-fips<6.8.0-78.78+fips1

6.8.0-78.78+fips1

ubuntu/linux-vmware*

Remediation

Recommended actions to resolve this vulnerability, in priority order.

Upgrade
Upgrade ubuntu/linux-aws to a version that resolves this vulnerability.
Fixed in 4.4.0-1148.154
Upgrade
Upgrade ubuntu/linux-azure to a version that resolves this vulnerability.
Fixed in 4.15.0-1193.208~14.04.1
Upgrade
Upgrade ubuntu/linux-lts-xenial to a version that resolves this vulnerability.
Fixed in 4.4.0-273.307~14.04.1
Upgrade
Upgrade ubuntu/linux to a version that resolves this vulnerability.
Fixed in 4.4.0-273.307
Upgrade
Upgrade ubuntu/linux-aws to a version that resolves this vulnerability.
Fixed in 4.4.0-1186.201
Upgrade
Upgrade ubuntu/linux-aws-hwe to a version that resolves this vulnerability.
Fixed in 4.15.0-1185.198~16.04.1
Upgrade
Upgrade ubuntu/linux-azure to a version that resolves this vulnerability.
Fixed in 4.15.0-1193.208~16.04.1
Upgrade
Upgrade ubuntu/linux-gcp to a version that resolves this vulnerability.
Fixed in 4.15.0-1178.195~16.04.1
Upgrade
Upgrade ubuntu/linux-hwe to a version that resolves this vulnerability.
Fixed in 4.15.0-242.254~16.04.1
Upgrade
Upgrade ubuntu/linux-kvm to a version that resolves this vulnerability.
Fixed in 4.4.0-1149.160
Upgrade
Upgrade ubuntu/linux-oracle to a version that resolves this vulnerability.
Fixed in 4.15.0-1148.159~16.04.1
Upgrade
Upgrade ubuntu/linux-fips to a version that resolves this vulnerability.
Fixed in 4.4.0-1119.126
Upgrade
Upgrade ubuntu/linux to a version that resolves this vulnerability.
Fixed in 4.15.0-242.254
Upgrade
Upgrade ubuntu/linux-aws to a version that resolves this vulnerability.
Fixed in 4.15.0-1185.198
Upgrade
Upgrade ubuntu/linux-aws-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1151.161~18.04.1
Upgrade
Upgrade ubuntu/linux-azure-4.15 to a version that resolves this vulnerability.
Fixed in 4.15.0-1193.208
Upgrade
Upgrade ubuntu/linux-azure-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1154.161~18.04.1
Upgrade
Upgrade ubuntu/linux-gcp-4.15 to a version that resolves this vulnerability.
Fixed in 4.15.0-1178.195
Upgrade
Upgrade ubuntu/linux-gcp-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1154.163~18.04.1
Upgrade
Upgrade ubuntu/linux-hwe-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-222.242~18.04.1
Upgrade
Upgrade ubuntu/linux-ibm-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1097.102~18.04.1
Upgrade
Upgrade ubuntu/linux-kvm to a version that resolves this vulnerability.
Fixed in 4.15.0-1168.173
Upgrade
Upgrade ubuntu/linux-oracle to a version that resolves this vulnerability.
Fixed in 4.15.0-1147.158
Upgrade
Upgrade ubuntu/linux-oracle-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1149.159~18.04.1
Upgrade
Upgrade ubuntu/linux-raspi-5.4 to a version that resolves this vulnerability.
Fixed in 5.4.0-1134.147~18.04.1
Upgrade
Upgrade ubuntu/linux-aws-fips to a version that resolves this vulnerability.
Fixed in 4.15.0-2123.129
Upgrade
Upgrade ubuntu/linux-azure-fips to a version that resolves this vulnerability.
Fixed in 4.15.0-2102.108
Upgrade
Upgrade ubuntu/linux-fips to a version that resolves this vulnerability.
Fixed in 4.15.0-1140.151
Upgrade
Upgrade ubuntu/linux-gcp-fips to a version that resolves this vulnerability.
Fixed in 4.15.0-2086.92
Upgrade
Upgrade ubuntu/linux-aws-5.15 to a version that resolves this vulnerability.
Fixed in 5.15.0-1084.91~20.04.1
Upgrade
Upgrade ubuntu/linux-azure-5.15 to a version that resolves this vulnerability.
Fixed in 5.15.0-1089.98~20.04.1
Upgrade
Upgrade ubuntu/linux-gcp-5.15 to a version that resolves this vulnerability.
Fixed in 5.15.0-1083.92~20.04.1
Upgrade
Upgrade ubuntu/linux-ibm-5.15 to a version that resolves this vulnerability.
Fixed in 5.15.0-1076.79~20.04.1
Upgrade
Upgrade ubuntu/linux-intel-iotg-5.15 to a version that resolves this vulnerability.
Fixed in 5.15.0-1079.85~20.04.1
Upgrade
Upgrade ubuntu/linux-lowlatency-hwe-5.15 to a version that resolves this vulnerability.
Fixed in 5.15.0-140.150~20.04.1
Upgrade
Upgrade ubuntu/linux-oracle-5.15 to a version that resolves this vulnerability.
Fixed in 5.15.0-1081.87~20.04.1
Upgrade
Upgrade ubuntu/linux-riscv-5.15 to a version that resolves this vulnerability.
Fixed in 5.15.0-1079.83~20.04.1
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Fixed in 5.15.0-1076.79
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Fixed in 6.8.0-1032.36
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Fixed in 6.8.0-1019.21
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Fixed in 6.11.0-26.26~24.04.1
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Fixed in 6.8.0-1033.33
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Fixed in 6.8.0-1035.38.1
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Fixed in 6.8.0-1009.9
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Fixed in 6.11.0-1022.22
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Fixed in 6.8.0-1035.39
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Fixed in 6.8.0-1017.18
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Fixed in 6.8.0-2028.29
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Fixed in 6.8.1-1030.31
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Fixed in 6.8.0-78.78+fips1
Compensating control
In the Linux kernel NFS server, clear acl_access and acl_default after calling posix_acl_release on them, including when retrieving acl_default fails and both ACL pointers are released simultaneously.

Event History

Feb 27, 2025

CVE Published

via OSV·03:15 AM

Data Sourced

via OSV·03:15 AM

DescriptionSeverityAffected Software

Frequently Asked Questions

Which deployments should be prioritized for investigation?

Prioritize Ubuntu systems using the listed Linux kernel packages where the NFS server daemon, nfsd, is running. The reported failure occurs in the NFSv3 ACL handling and release path, specifically nfs3svc_release_getacl.

What condition leads to the use-after-free warning?

The issue is triggered when obtaining acl_default fails after acl_access and acl_default are released together. The acl_access pointer is not cleared and can still reference the released POSIX ACL.

How can administrators identify a potentially affected runtime event?

Check kernel logs for a refcount underflow or use-after-free warning associated with nfsd, particularly a stack trace naming nfs3svc_release_getacl. The reported warning originates from refcount_warn_saturate in lib/refcount.c.

UBUNTU-CVE-2025-21796: Use After Free

Affected Software

Remediation

Event History

Frequently Asked Questions

Which deployments should be prioritized for investigation?

What condition leads to the use-after-free warning?

How can administrators identify a potentially affected runtime event?

Company

Resources

Contact

Frequently Asked Questions

Which deployments should be prioritized for investigation?

What condition leads to the use-after-free warning?

How can administrators identify a potentially affected runtime event?