NVD / CVE Program· CNA Linux

CVE-2021-47375: blktrace: Fix uaf in blk_trace access after removing by sysfs

Noroxi assessment

Priority: Monitor (action score 24/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.25% (FIRST EPSS).
Someone with local access to the system can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
Fixed version: Linux Linux 3815fe7371d2411ce164281cef40d9fc7b323dee, 488da313edf3abea7f7733efe011c96b23740ab5, 5afedf670caf30a2b5a52da96eb7eac7dee6a9c9.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 3815fe7371d2411ce164281cef40d9fc7b323dee, 488da313edf3abea7f7733efe011c96b23740ab5, 5afedf670caf30a2b5a52da96eb7eac7dee6a9c9 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: blktrace: Fix uaf in blk_trace access after removing by sysfs There is an use-after-free problem triggered by following process: P1(sda) P2(sdb) echo 0 > /sys/block/sdb/trace/enable blk_trace_remove_queue synchronize_rcu blk_trace_free relay_close rcu_read_lock __blk_add_trace trace_note_tsk (Iterate running_trace_list) relay_close_buf relay_destroy_buf kfree(buf) trace_note(sdb's bt) relay_reserve buf->offset <- nullptr deference (use-after-free) !!! rcu_read_unlock [ 502.714379] BUG: kernel NULL pointer dereference, address: 0000000000000010 [ 502.715260] #PF: supervisor read access in kernel mode [ 502.715903] #PF: error_code(0x0000) - not-present page [ 502.716546] PGD 103984067 P4D 103984067 PUD 17592b067 PMD 0 [ 502.717252] Oops: 0000 [#1] SMP [ 502.720308] RIP: 0010:trace_note.isra.0+0x86/0x360 [ 502.732872] Call Trace: [ 502.733193] __blk_add_trace.cold+0x137/0x1a3 [ 502.733734] blk_add_trace_rq+0x7b/0xd0 [ 502.734207] blk_add_trace_rq_issue+0x54/0xa0 [ 502.734755] blk_mq_start_request+0xde/0x1b0 [ 502.735287] scsi_queue_rq+0x528/0x1140 ... [ 502.742704] sg_new_write.isra.0+0x16e/0x3e0 [ 502.747501] sg_ioctl+0x466/0x1100 Reproduce method: ioctl(/dev/sda, BLKTRACESETUP, blk_user_trace_setup[buf_size=127]) ioctl(/dev/sda, BLKTRACESTART) ioctl(/dev/sdb, BLKTRACESETUP, blk_user_trace_setup[buf_size=127]) ioctl(/dev/sdb, BLKTRACESTART) echo 0 > /sys/block/sdb/trace/enable & // Add delay(mdelay/msleep) before kernel enters blk_trace_free() ioctl$SG_IO(/dev/sda, SG_IO, ...) // Enters trace_note_tsk() after blk_trace_free() returned // Use mdelay in rcu region rather than msleep(which may schedule out) Remove blk_trace from running_list before calling blk_trace_free() by sysfs if blk_trace is at Blktrace_running state.

MediumCVSS 6.2 · v3.1—No exploit Fix available

Memory safety

Published: May 21, 2024
Updated: Jun 17, 2026
EPSS: 0.2% · 16th percentile
CWE: CWE-416

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 24 / 40 · 6.2 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Running WordPress? Scan your site free with WP Lens

Is your version affected? Check it

Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

We use this product, ask for help

Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
linux	linux kernel	cpe:2.3:o:linux:linux_kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

linux linux kernel2.6.30 and later · before 4.4.286
linux linux kernel4.5 and later · before 4.9.285
linux linux kernel4.10 and later · before 4.14.249
linux linux kernel4.15 and later · before 4.19.209
linux linux kernel4.20 and later · before 5.4.150
linux linux kernel5.5 and later · before 5.10.70
linux linux kernel5.11 and later · before 5.14.9
linux linux kernel5.15

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

Linux Linux
- 2.6.30affected
- c71a896154119f4ca9e89d6078f5f63ad60ef199 and later · before 488da313edf3abea7f7733efe011c96b23740ab5affected · git
- c71a896154119f4ca9e89d6078f5f63ad60ef199 and later · before dacfd5e4d1142bfb3809aab3634a375f6f373269affected · git
- c71a896154119f4ca9e89d6078f5f63ad60ef199 and later · before d56171d9360c0170c5c5f8f7e2362a2e999eca40affected · git
- c71a896154119f4ca9e89d6078f5f63ad60ef199 and later · before 677e362ba807f3aafe6f405c07e0b37244da5222affected · git
- c71a896154119f4ca9e89d6078f5f63ad60ef199 and later · before ebb8d26d93c3ec3c7576c52a8373a2309423c069affected · git
- c71a896154119f4ca9e89d6078f5f63ad60ef199 and later · before 3815fe7371d2411ce164281cef40d9fc7b323deeaffected · git
- c71a896154119f4ca9e89d6078f5f63ad60ef199 and later · before a5f8e86192612d0183047448d8bbe7918b3f1a26affected · git
- c71a896154119f4ca9e89d6078f5f63ad60ef199 and later · before 5afedf670caf30a2b5a52da96eb7eac7dee6a9c9affected · git
- before 2.6.30not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	linux	before 5.14.9-1	5.14.9-1
openSUSE:Leap Micro 5.3	kernel-rt	before 5.14.21-150400.15.82.1	5.14.21-150400.15.82.1
SUSE:Linux Enterprise Micro 5.3	kernel-rt	before 5.14.21-150400.15.82.1	5.14.21-150400.15.82.1
SUSE:Linux Enterprise Micro 5.3	kernel-source-rt	before 5.14.21-150400.15.82.1	5.14.21-150400.15.82.1

Same product

linux: all records

Other highest-scoring records for the same primary product.

CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
90Now
CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
89Now
CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
85Now

Published before and after this one in the same product

← EarlierCVE-2021-47373May 21, 2024 · irqchip/gic-v3-its: Fix potential VPE leak on error
22Monitor
← EarlierCVE-2021-47374May 21, 2024 · dma-debug: prevent an error message from causing runtime problems
22Monitor
Later →CVE-2021-47376May 21, 2024 · bpf: Add oversize check before call kvcalloc()
22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
Linux Linux	3815fe7371d2411ce164281cef40d9fc7b323dee	Vendor (CNA)
Linux Linux	488da313edf3abea7f7733efe011c96b23740ab5	Vendor (CNA)
Linux Linux	5afedf670caf30a2b5a52da96eb7eac7dee6a9c9	Vendor (CNA)
Linux Linux	677e362ba807f3aafe6f405c07e0b37244da5222	Vendor (CNA)
Linux Linux	a5f8e86192612d0183047448d8bbe7918b3f1a26	Vendor (CNA)
Linux Linux	d56171d9360c0170c5c5f8f7e2362a2e999eca40	Vendor (CNA)
Linux Linux	dacfd5e4d1142bfb3809aab3634a375f6f373269	Vendor (CNA)
Linux Linux	ebb8d26d93c3ec3c7576c52a8373a2309423c069	Vendor (CNA)
debian:linux	5.14.9-1 · Debian:12	Package registry (OSV)
opensuse:kernel-rt	5.14.21-150400.15.82.1 · openSUSE:Leap Micro 5.3	Package registry (OSV)
suse:kernel-rt	5.14.21-150400.15.82.1 · SUSE:Linux Enterprise Micro 5.3	Package registry (OSV)
suse:kernel-source-rt	5.14.21-150400.15.82.1 · SUSE:Linux Enterprise Micro 5.3	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

TR-24-0519 · May 22, 2024(Linux Kernel Güncellemesi)

All national notices →

Technical details

Attack conditions

Someone with local access to the system can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: none
Availability: none

Attack vector: Local
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: None
Availability impact: None

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

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

nvd-secondary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

Fix✗ → ✓Sep 28, 2026, 10:11 PM UTC

For records you follow, these changes also arrive as notifications. →

References

git.kernel.org/stable/c/3815fe7371d2411ce164281cef40d9fc7b323dee

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records