CVE-2021-47634

HIGHNVD 7.87.8
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to NVD's CVSS score.

Score 7.8 from GitHub Security Advisory (severity: HIGH) published 2025-02-27. NVD baseline CVSS 7.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, NVD CVSS v3
Trending — 3 sources updated this week

Also known asEUVD-2021-34670 (ENISA EUVD) · GHSA-j4hc-7ppm-rrh4 (GitHub Security Advisories)Source: ENISA EUVD

7.8EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 7.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

In the Linux kernel, the following vulnerability has been resolved:

ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl

Hulk Robot reported a KASAN report about use-after-free: ================================================================== BUG: KASAN: use-after-free in __list_del_entry_valid+0x13d/0x160 Read of size 8 at addr ffff888035e37d98 by task ubiattach/1385 [...] Call Trace: klist_dec_and_del+0xa7/0x4a0 klist_put+0xc7/0x1a0 device_del+0x4d4/0xed0 cdev_device_del+0x1a/0x80 ubi_attach_mtd_dev+0x2951/0x34b0 [ubi] ctrl_cdev_ioctl+0x286/0x2f0 [ubi]

Allocated by task 1414: device_add+0x60a/0x18b0 cdev_device_add+0x103/0x170 ubi_create_volume+0x1118/0x1a10 [ubi] ubi_cdev_ioctl+0xb7f/0x1ba0 [ubi]

Freed by task 1385: cdev_device_del+0x1a/0x80 ubi_remove_volume+0x438/0x6c0 [ubi] ubi_cdev_ioctl+0xbf4/0x1ba0 [ubi] [...] ==================================================================

The lock held by ctrl_cdev_ioctl is ubi_devices_mutex, but the lock held by ubi_cdev_ioctl is ubi->device_mutex. Therefore, the two locks can be concurrent.

ctrl_cdev_ioctl contains two operations: ubi_attach and ubi_detach. ubi_detach is bug-free because it uses reference counting to prevent concurrency. However, uif_init and uif_close in ubi_attach may race with ubi_cdev_ioctl.

uif_init will race with ubi_cdev_ioctl as in the following stack. cpu1 cpu2 cpu3 _______________________|________________________|______________________ ctrl_cdev_ioctl ubi_attach_mtd_dev uif_init ubi_cdev_ioctl ubi_create_volume cdev_device_add ubi_add_volume // sysfs exist kill_volumes ubi_cdev_ioctl ubi_remove_volume cdev_device_del // first free ubi_free_volume cdev_del // double free cdev_device_del

And uif_close will race with ubi_cdev_ioctl as in the following stack. cpu1 cpu2 cpu3 _______________________|________________________|______________________ ctrl_cdev_ioctl ubi_attach_mtd_dev uif_init ubi_cdev_ioctl ubi_create_volume cdev_device_add ubi_debugfs_init_dev //error goto out_uif; uif_close kill_volumes ubi_cdev_ioctl ubi_remove_volume cdev_device_del // first free ubi_free_volume // double free

The cause of this problem is that commit 714fb87e8bc0 make device "available" before it becomes accessible via sysfs. Therefore, we roll back the modification. We will fix the race condition between ubi device creation and udev by removing ubi_get_device in vol_attribute_show and dev_attribute_show.This avoids accessing uninitialized ubi_devices[ubi_num].

ubi_get_device is used to prevent devices from being deleted during sysfs execution. However, now kernfs ensures that devices will not be deleted before all reference counting are released. The key process is shown in the following stack.

device_del device_remove_attrs device_remove_groups sysfs_remove_groups sysfs_remove_group remove_files kernfs_remove_by_name kernfs_remove_by_name_ns __kernfs_remove kernfs_drain

CVSS v3
7.8
EG Score
7.8HIGHmedium confidence
EG Risk
35
EG Risk 35/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity78% × 45%
Impact severity (EG Severity): CVSS 7.8 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.3% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Track* at high (mission-essential systems).
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.3%
EPSS %ILE
21st
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (7.8): severity, escalated by confirmed exploitation. This CVE's 7.8 is its impact severity (EG Severity), not escalated.

EG Severity
7.8 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
0.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-27). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

February 26, 2025

Last Modified

March 24, 2025

Advisory Details (8)

Auto-updated Oct 28, 2026
Patch available.
Web page

ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/f149b1bd213820363731aa119e5011ca892a2aac
Web page

ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/d727fd32cbd1abf3465f607021bc9c746f17b5a8
Web page

ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/c32fe764191b8ae8b128588beb96e3718d9179d8
Web page

ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/a8ecee49259f8f78d91ddb329ab2be7e6fd01974
Web page

ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/5f9e9c223e48c264241d2f34d0bfc29e5fcb5c1b
Web page

ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/432b057f8e847ae5a2306515606f8d2defaca178
Web page

ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/3cbf0e392f173ba0ce425968c8374a6aa3e90f2e
Web page

ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/1a3f1cf87054833242fcd0218de0481cf855f888

Patch Availability(2)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
ubuntulinux-virtual-lts-xenial (4.4.0.276.282) @ xenial2026-10-21ubuntu
ubuntulinux-tools-fips (4.4.0.1120.121) @ xenial2026-10-21ubuntu

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(4 across 4 ecosystems)
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
linux5.10.103-1 ... 5.10.92-2 (11 versions)
  • every version up to 5.10.113-1: fixed in 5.10.113-1
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
linux—
  • every version up to 5.17.3-1: fixed in 5.17.3-1
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
linux—
  • every version up to 5.17.3-1: fixed in 5.17.3-1
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
linux—
  • every version up to 5.17.3-1: fixed in 5.17.3-1
—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(2)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 9× in last 7d / 39× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 97 of 199 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 3 repeat rows among the latest 100 are merged into the row they repeat. The 102 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-11-02 16:38 UTCEPSS rescoreEPSS 0.3% · 21st percentile
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  3. 2026-10-31 16:29 UTCEPSS rescoreEPSS 0.3% · 21st percentile
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  6. 2026-10-28 16:28 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  7. 2026-10-28 02:12 UTCEG score recompute
  8. 2026-10-28 02:12 UTCGHSA enrichmentGHSA-j4hc-7ppm-rrh4 · GitHub severity HIGH · GitHub CVSS 7.8
  9. 2026-10-27 16:28 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  10. 2026-10-26 16:28 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  11. 2026-10-25 18:18 UTCEG score recompute
  12. 2026-10-25 16:29 UTCEPSS rescoreEPSS 0.3% · 21st percentile
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  17. 2026-10-21 08:31 UTCEG score recompute
  18. 2026-10-21 08:31 UTCVendor advisory
  19. 2026-10-21 08:31 UTCGHSA enrichmentGHSA-j4hc-7ppm-rrh4 · GitHub severity HIGH · GitHub CVSS 7.8
  20. 2026-10-20 16:28 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  21. 2026-10-19 16:28 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  22. 2026-10-18 16:28 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  23. 2026-10-18 08:49 UTCEG score recompute
  24. 2026-10-17 16:29 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  25. 2026-10-16 16:34 UTCEPSS rescoreEPSS 0.3% · 20th percentile
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  1. 2026-10-15 16:28 UTCEPSS rescoreEPSS 0.3% · 20th percentile
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  3. 2026-10-13 16:28 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  4. 2026-10-12 19:05 UTCEG score recompute
  5. 2026-10-12 16:30 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  6. 2026-10-11 23:31 UTCEG score recompute
  7. 2026-10-11 13:44 UTCEPSS rescoreEPSS 0.3% · 20th percentile
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  16. 2026-10-02 22:10 UTCOSV refresh
  17. 2026-10-02 16:23 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  18. 2026-09-30 15:45 UTCEG score recompute
  19. 2026-09-30 15:00 UTCEPSS rescoreEPSS 0.3% · 19th percentile
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  34. 2026-09-13 19:39 UTCOSV refresh
  35. 2026-09-12 14:57 UTCEPSS rescoreEPSS 0.3% · 21st percentile
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  65. 2026-08-09 14:09 UTCOSV refresh
  66. 2026-08-09 13:44 UTCEPSS rescoreEPSS 0.3% · 21st percentile
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Frequently asked(5)

What is CVE-2021-47634?
CVE-2021-47634 is a high-severity vulnerability; its CVE record was published on February 26, 2025. In the Linux kernel, the following vulnerability has been resolved: ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl Hulk Robot reported a KASAN report about use-after-free: ================================================================== BUG: KASAN: use-after-free in…
When was the CVE record for CVE-2021-47634 published?
The CVE record for CVE-2021-47634 was published on February 26, 2025. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of March 24, 2025; the record at its source may have been updated since.
Is CVE-2021-47634 actively exploited?
CVE-2021-47634 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (21st percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-47634?
CVE-2021-47634 has a CVSS v3 base score of 7.8 (NVD).
How do I remediate CVE-2021-47634?
A fix for CVE-2021-47634 is available: update to the fixed version the vendor names in its advisory.

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