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Linux Distros Unpatched Vulnerability : CVE-2021-46957

medium Nessus Plugin ID 244012

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Synopsis

The Linux/Unix host has one or more packages installed with a vulnerability that the vendor indicates will not be patched.

Description

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

 - In the Linux kernel, the following vulnerability has been resolved: riscv/kprobe: fix kernel panic when invoking sys_read traced by kprobe The execution of sys_read end up hitting a BUG_ON() in __find_get_block after installing kprobe at sys_read, the BUG message like the following: [ 65.708663] ------------[ cut here ]------------ [ 65.709987] kernel BUG at fs/buffer.c:1251! [ 65.711283] Kernel BUG [#1] [ 65.712032] Modules linked in: [ 65.712925] CPU: 0 PID: 51 Comm: sh Not tainted 5.12.0-rc4 #1 [ 65.714407] Hardware name: riscv-virtio,qemu (DT) [ 65.715696] epc : __find_get_block+0x218/0x2c8 [ 65.716835] ra :
 __getblk_gfp+0x1c/0x4a [ 65.717831] epc : ffffffe00019f11e ra : ffffffe00019f56a sp : ffffffe002437930 [ 65.719553] gp : ffffffe000f06030 tp : ffffffe0015abc00 t0 : ffffffe00191e038 [ 65.721290] t1 :
 ffffffe00191e038 t2 : 000000000000000a s0 : ffffffe002437960 [ 65.723051] s1 : ffffffe00160ad00 a0 :
 ffffffe00160ad00 a1 : 000000000000012a [ 65.724772] a2 : 0000000000000400 a3 : 0000000000000008 a4 :
 0000000000000040 [ 65.726545] a5 : 0000000000000000 a6 : ffffffe00191e000 a7 : 0000000000000000 [ 65.728308] s2 : 000000000000012a s3 : 0000000000000400 s4 : 0000000000000008 [ 65.730049] s5 :
 000000000000006c s6 : ffffffe00240f800 s7 : ffffffe000f080a8 [ 65.731802] s8 : 0000000000000001 s9 :
 000000000000012a s10: 0000000000000008 [ 65.733516] s11: 0000000000000008 t3 : 00000000000003ff t4 :
 000000000000000f [ 65.734434] t5 : 00000000000003ff t6 : 0000000000040000 [ 65.734613] status:
 0000000000000100 badaddr: 0000000000000000 cause: 0000000000000003 [ 65.734901] Call Trace: [ 65.735076] [<ffffffe00019f11e>] __find_get_block+0x218/0x2c8 [ 65.735417] [<ffffffe00020017a>]
 __ext4_get_inode_loc+0xb2/0x2f6 [ 65.735618] [<ffffffe000201b6c>] ext4_get_inode_loc+0x3a/0x8a [ 65.735802] [<ffffffe000203380>] ext4_reserve_inode_write+0x2e/0x8c [ 65.735999] [<ffffffe00020357a>]
 __ext4_mark_inode_dirty+0x4c/0x18e [ 65.736208] [<ffffffe000206bb0>] ext4_dirty_inode+0x46/0x66 [ 65.736387] [<ffffffe000192914>] __mark_inode_dirty+0x12c/0x3da [ 65.736576] [<ffffffe000180dd2>] touch_atime+0x146/0x150 [ 65.736748] [<ffffffe00010d762>] filemap_read+0x234/0x246 [ 65.736920] [<ffffffe00010d834>] generic_file_read_iter+0xc0/0x114 [ 65.737114] [<ffffffe0001f5d7a>] ext4_file_read_iter+0x42/0xea [ 65.737310] [<ffffffe000163f2c>] new_sync_read+0xe2/0x15a [ 65.737483] [<ffffffe000165814>] vfs_read+0xca/0xf2 [ 65.737641] [<ffffffe000165bae>] ksys_read+0x5e/0xc8 [ 65.737816] [<ffffffe000165c26>] sys_read+0xe/0x16 [ 65.737973] [<ffffffe000003972>] ret_from_syscall+0x0/0x2 [ 65.738858] ---[ end trace fe93f985456c935d ]--- A simple reproducer looks like: echo 'p:myprobe sys_read fd=%a0 buf=%a1 count=%a2' > /sys/kernel/debug/tracing/kprobe_events echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable cat /sys/kernel/debug/tracing/trace Here's what happens to hit that BUG_ON(): 1) After installing kprobe at entry of sys_read, the first instruction is replaced by 'ebreak' instruction on riscv64 platform. 2) Once kernel reach the 'ebreak' instruction at the entry of sys_read, it trap into the riscv breakpoint handler, where it do something to setup for coming single-step of origin instruction, including backup the 'sstatus' in pt_regs, followed by disable interrupt during single stepping via clear 'SIE' bit of 'sstatus' in pt_regs. 3) Then kernel restore to the instruction slot contains two instructions, one is original instruction at entry of sys_read, the other is 'ebreak'. Here it trigger a 'Instruction page fault' exception (value at 'scause' is '0xc'), if PF is not filled into PageTabe for that slot yet. 4) Again kernel trap into page fault exception handler, where it choose different policy according to the state of running kprobe. Because afte 2) the state is KPROBE_HIT_SS, so kernel reset the current kp ---truncated--- (CVE-2021-46957)

Note that Nessus relies on the presence of the package as reported by the vendor.

Solution

There is no known solution at this time.

See Also

https://ubuntu.com/security/CVE-2021-46957

Plugin Details

Severity: Medium

ID: 244012

File Name: unpatched_CVE_2021_46957.nasl

Version: 1.1

Type: local

Agent: unix

Family: Misc.

Published: 8/6/2025

Updated: 8/6/2025

Supported Sensors: Frictionless Assessment AWS, Frictionless Assessment Azure, Frictionless Assessment Agent, Nessus Agent, Agentless Assessment, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.4

CVSS v2

Risk Factor: Medium

Base Score: 6.6

Temporal Score: 4.9

Vector: CVSS2#AV:L/AC:L/Au:N/C:C/I:N/A:C

CVSS Score Source: CVE-2021-46957

CVSS v3

Risk Factor: Medium

Base Score: 5.5

Temporal Score: 4.8

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

CPE: cpe:/o:canonical:ubuntu_linux:20.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-lowlatency-hwe-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-gke-4.15, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.3, p-cpe:/a:canonical:ubuntu_linux:linux-gke-5.15, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-oem-6.0, p-cpe:/a:canonical:ubuntu_linux:linux-hwe, p-cpe:/a:canonical:ubuntu_linux:linux-azure-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-azure-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-azure-5.3, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-nvidia-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-oracle-5.0, p-cpe:/a:canonical:ubuntu_linux:linux-oem-5.6, p-cpe:/a:canonical:ubuntu_linux:linux-aws-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-raspi2, p-cpe:/a:canonical:ubuntu_linux:linux-gke, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-5.19, cpe:/o:canonical:ubuntu_linux:18.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:linux-gkeop-5.4, p-cpe:/a:canonical:ubuntu_linux:linux-intel-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-oracle-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-gke-5.4, p-cpe:/a:canonical:ubuntu_linux:linux-oem, p-cpe:/a:canonical:ubuntu_linux:linux-oracle-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-oem-5.17, p-cpe:/a:canonical:ubuntu_linux:linux-riscv-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-azure-edge, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.0, p-cpe:/a:canonical:ubuntu_linux:linux-lowlatency-hwe-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-allwinner-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-5.8, p-cpe:/a:canonical:ubuntu_linux:linux-starfive-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-oem-5.14, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-oem-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-gcp, p-cpe:/a:canonical:ubuntu_linux:linux-azure-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-5.3, p-cpe:/a:canonical:ubuntu_linux:linux-gcp-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-azure-fde, p-cpe:/a:canonical:ubuntu_linux:linux-azure, cpe:/o:canonical:ubuntu_linux:16.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:linux-azure-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-azure-fde-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-oracle-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-riscv-5.11, p-cpe:/a:canonical:ubuntu_linux:linux-riscv-5.19, p-cpe:/a:canonical:ubuntu_linux:linux-oracle-5.3, p-cpe:/a:canonical:ubuntu_linux:linux-hwe-edge, p-cpe:/a:canonical:ubuntu_linux:linux-starfive-6.2, cpe:/o:canonical:ubuntu_linux:22.04:-:lts, p-cpe:/a:canonical:ubuntu_linux:linux-oem-6.1, p-cpe:/a:canonical:ubuntu_linux:linux-azure-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-aws-5.13, p-cpe:/a:canonical:ubuntu_linux:linux-riscv, p-cpe:/a:canonical:ubuntu_linux:linux-azure-fde-6.2, p-cpe:/a:canonical:ubuntu_linux:linux-oem-5.10

Required KB Items: Host/local_checks_enabled, Host/cpu, global_settings/vendor_unpatched, Host/OS/identifier

Exploit Ease: No known exploits are available

Vulnerability Publication Date: 2/27/2024

Reference Information

CVE: CVE-2021-46957