CVE-2021-46957

MEDIUMNVD 5.55.5—
EchelonGraph scoreMEDIUM confidence

Score 5.5 from GitHub Security Advisory published 2024-02-27. NVD baseline CVSS 5.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
5.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.5Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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] [] __find_get_block+0x218/0x2c8 [ 65.735417] [] __ext4_get_inode_loc+0xb2/0x2f6 [ 65.735618] [] ext4_get_inode_loc+0x3a/0x8a [ 65.735802] [] ext4_reserve_inode_write+0x2e/0x8c [ 65.735999] [] __ext4_mark_inode_dirty+0x4c/0x18e [ 65.736208] [] ext4_dirty_inode+0x46/0x66 [ 65.736387] [] __mark_inode_dirty+0x12c/0x3da [ 65.736576] [] touch_atime+0x146/0x150 [ 65.736748] [] filemap_read+0x234/0x246 [ 65.736920] [] generic_file_read_iter+0xc0/0x114 [ 65.737114] [] ext4_file_read_iter+0x42/0xea [ 65.737310] [] new_sync_read+0xe2/0x15a [ 65.737483] [] vfs_read+0xca/0xf2 [ 65.737641] [] ksys_read+0x5e/0xc8 [ 65.737816] [] sys_read+0xe/0x16 [ 65.737973] [] 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---

CVSS v3
5.5
EG Score
5.5(medium)
EG Risk
25(Track)
EG Risk 25/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity55% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
11%
KEV
Not listed

Published

February 27, 2024

Last Modified

March 14, 2025

References (4)

Data Freshness Timeline

(refreshed 7× in last 7d / 38× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 113 total refreshes for this CVE.

  1. 2026-08-07 16:24 UTCEPSS rescore
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Frequently asked(5)

What is CVE-2021-46957?
CVE-2021-46957 is a medium vulnerability published on February 27, 2024. 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 sysread end up hitting a BUGON() in findgetblock after installing kprobe at sys_read, the BUG message like the following: [ 65.708663]…
When was CVE-2021-46957 disclosed?
CVE-2021-46957 was first published in the National Vulnerability Database on February 27, 2024, with the most recent update on March 14, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-46957 actively exploited?
CVE-2021-46957 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 89.0% of all scored CVEs.
What is the CVSS score of CVE-2021-46957?
CVE-2021-46957 has a CVSS v3 base score of 5.5 (NVD).
How do I remediate CVE-2021-46957?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-46957, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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