CVE-2021-47656

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-2021-34649 (ENISA EUVD) · GHSA-4mx7-h455-mwxv (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:

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem

When we mount a jffs2 image, assume that the first few blocks of the image are normal and contain at least one xattr-related inode, but the next block is abnormal. As a result, an error is returned in jffs2_scan_eraseblock(). jffs2_clear_xattr_subsystem() is then called in jffs2_build_filesystem() and then again in jffs2_do_fill_super().

Finally we can observe the following report: ================================================================== BUG: KASAN: use-after-free in jffs2_clear_xattr_subsystem+0x95/0x6ac Read of size 8 at addr ffff8881243384e0 by task mount/719

Call Trace: dump_stack+0x115/0x16b jffs2_clear_xattr_subsystem+0x95/0x6ac jffs2_do_fill_super+0x84f/0xc30 jffs2_fill_super+0x2ea/0x4c0 mtd_get_sb+0x254/0x400 mtd_get_sb_by_nr+0x4f/0xd0 get_tree_mtd+0x498/0x840 jffs2_get_tree+0x25/0x30 vfs_get_tree+0x8d/0x2e0 path_mount+0x50f/0x1e50 do_mount+0x107/0x130 __se_sys_mount+0x1c5/0x2f0 __x64_sys_mount+0xc7/0x160 do_syscall_64+0x45/0x70 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Allocated by task 719: kasan_save_stack+0x23/0x60 __kasan_kmalloc.constprop.0+0x10b/0x120 kasan_slab_alloc+0x12/0x20 kmem_cache_alloc+0x1c0/0x870 jffs2_alloc_xattr_ref+0x2f/0xa0 jffs2_scan_medium.cold+0x3713/0x4794 jffs2_do_mount_fs.cold+0xa7/0x2253 jffs2_do_fill_super+0x383/0xc30 jffs2_fill_super+0x2ea/0x4c0 [...]

Freed by task 719: kmem_cache_free+0xcc/0x7b0 jffs2_free_xattr_ref+0x78/0x98 jffs2_clear_xattr_subsystem+0xa1/0x6ac jffs2_do_mount_fs.cold+0x5e6/0x2253 jffs2_do_fill_super+0x383/0xc30 jffs2_fill_super+0x2ea/0x4c0 [...]

The buggy address belongs to the object at ffff8881243384b8 which belongs to the cache jffs2_xattr_ref of size 48 The buggy address is located 40 bytes inside of 48-byte region [ffff8881243384b8, ffff8881243384e8) [...] ==================================================================

The triggering of the BUG is shown in the following stack: ----------------------------------------------------------- jffs2_fill_super jffs2_do_fill_super jffs2_do_mount_fs jffs2_build_filesystem jffs2_scan_medium jffs2_scan_eraseblock <--- ERROR jffs2_clear_xattr_subsystem <--- free jffs2_clear_xattr_subsystem <--- free again -----------------------------------------------------------

An error is returned in jffs2_do_mount_fs(). If the error is returned by jffs2_sum_init(), the jffs2_clear_xattr_subsystem() does not need to be executed. If the error is returned by jffs2_build_filesystem(), the jffs2_clear_xattr_subsystem() also does not need to be executed again. So move jffs2_clear_xattr_subsystem() from 'out_inohash' to 'out_root' to fix this UAF problem.

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
17th
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 2026-10-28). 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

August 5, 2026

Advisory Details (9)

Auto-updated Aug 5, 2026
Patch available.
Web page

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/4c7c44ee1650677fbe89d86edbad9497b7679b5c
Web page

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/8c0f024f29e055840a5a89fe23b96ae3f921afed
Web page

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/22327bd7988f21de3a53c1373f3b81542bfe1f44
Web page

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/7a75740206af5f17e9f3efa384211cba70213da1
Web page

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/7bb7428dd73991bf4b3a7a61b493ca50046c2b13
Web page

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/30bf7244acf32f19cb722c39f7bc1c2a9f300422
Web page

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/c3b07c875fa8f906f932976460fd14798596f101
Web page

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/3bd2454162ec6bbb5503233c804fce6e4b6dcec5
Web page

jffs2: fix use-after-free in jffs2_clear_xattr_subsystem - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/9150cb625b46f68d524f4cfd491f1aafc23e10a9

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.

Data Freshness Timeline

(refreshed 9× in last 7d / 38× 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 207 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 110 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% · 17th percentile
  2. 2026-11-01 16:30 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  3. 2026-10-31 16:29 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  4. 2026-10-30 16:30 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  5. 2026-10-29 16:29 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  6. 2026-10-29 00:10 UTCEG score recompute
  7. 2026-10-29 00:10 UTCGHSA enrichmentGHSA-4mx7-h455-mwxv · GitHub severity HIGH · GitHub CVSS 7.8
  8. 2026-10-28 16:28 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  9. 2026-10-27 16:28 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  10. 2026-10-26 16:28 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  11. 2026-10-25 18:18 UTCEG score recompute
  12. 2026-10-25 16:29 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  13. 2026-10-24 16:29 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  14. 2026-10-23 16:28 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  15. 2026-10-21 16:28 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  16. 2026-10-21 08:31 UTCEG score recompute
  17. 2026-10-21 08:31 UTCGHSA enrichmentGHSA-4mx7-h455-mwxv · GitHub severity HIGH · GitHub CVSS 7.8
  18. 2026-10-20 16:28 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  19. 2026-10-19 16:28 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  20. 2026-10-19 11:55 UTCOSV refresh
  21. 2026-10-18 16:28 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  22. 2026-10-18 08:49 UTCEG score recompute
  23. 2026-10-17 16:29 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  24. 2026-10-16 16:34 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  25. 2026-10-15 16:28 UTCEPSS rescoreEPSS 0.3% · 16th percentile
Show 72 more
  1. 2026-10-14 16:29 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  2. 2026-10-13 16:28 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  3. 2026-10-12 19:05 UTCEG score recompute
  4. 2026-10-12 16:30 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  5. 2026-10-11 23:30 UTCEG score recompute
  6. 2026-10-11 13:44 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  7. 2026-10-10 19:56 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  8. 2026-10-09 20:04 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  9. 2026-10-08 16:40 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  10. 2026-10-07 23:45 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  11. 2026-10-06 15:14 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  12. 2026-10-05 17:40 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  13. 2026-10-04 23:19 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  14. 2026-10-03 14:22 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  15. 2026-10-02 16:23 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  16. 2026-09-30 15:45 UTCEG score recompute
  17. 2026-09-30 15:00 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  18. 2026-09-29 15:15 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  19. 2026-09-28 13:47 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  20. 2026-09-26 19:03 UTCOSV refresh
  21. 2026-09-26 15:54 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  22. 2026-09-26 00:21 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  23. 2026-09-24 14:00 UTCEPSS rescoreEPSS 0.3% · 15th percentile
  24. 2026-09-23 13:45 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  25. 2026-09-22 14:44 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  26. 2026-09-21 20:28 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  27. 2026-09-20 20:13 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  28. 2026-09-19 15:38 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  29. 2026-09-18 19:24 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  30. 2026-09-17 19:23 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  31. 2026-09-16 14:05 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  32. 2026-09-15 03:06 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  33. 2026-09-12 14:57 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  34. 2026-09-11 14:49 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  35. 2026-09-11 09:33 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  36. 2026-09-08 21:57 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  37. 2026-09-07 15:58 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  38. 2026-09-07 04:48 UTCOSV refresh
  39. 2026-09-06 13:45 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  40. 2026-09-05 15:25 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  41. 2026-09-04 13:57 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  42. 2026-09-04 05:03 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  43. 2026-09-02 14:09 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  44. 2026-09-01 13:51 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  45. 2026-08-30 19:14 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  46. 2026-08-30 01:19 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  47. 2026-08-28 21:38 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  48. 2026-08-27 14:22 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  49. 2026-08-26 14:43 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  50. 2026-08-25 13:46 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  51. 2026-08-24 14:13 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  52. 2026-08-21 23:46 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  53. 2026-08-20 22:52 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  54. 2026-08-20 14:31 UTCOSV refresh
  55. 2026-08-19 17:01 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  56. 2026-08-18 13:45 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  57. 2026-08-17 13:44 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  58. 2026-08-16 14:53 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  59. 2026-08-16 02:11 UTCEPSS rescoreEPSS 0.3% · 17th percentile
  60. 2026-08-15 01:27 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  61. 2026-08-13 21:57 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  62. 2026-08-12 13:48 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  63. 2026-08-11 13:38 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  64. 2026-08-09 13:44 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  65. 2026-08-08 16:34 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  66. 2026-08-07 16:24 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  67. 2026-08-06 13:44 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  68. 2026-08-05 19:15 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  69. 2026-08-05 09:35 UTCEG score recompute
  70. 2026-08-05 09:35 UTCGHSA enrichmentGHSA-4mx7-h455-mwxv · GitHub severity HIGH · GitHub CVSS 7.8
  71. 2026-08-04 15:06 UTCEPSS rescoreEPSS 0.3% · 16th percentile
  72. 2026-08-04 11:17 UTCEG score recompute

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2021-47656?
CVE-2021-47656 is a high-severity vulnerability; its CVE record was published on February 26, 2025. In the Linux kernel, the following vulnerability has been resolved: jffs2: fix use-after-free in jffs2_clear_xattr_subsystem When we mount a jffs2 image, assume that the first few blocks of the image are normal and contain at least one xattr-related inode, but the next block is abnormal. As a…
When was the CVE record for CVE-2021-47656 published?
The CVE record for CVE-2021-47656 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 August 5, 2026; the record at its source may have been updated since.
Is CVE-2021-47656 actively exploited?
CVE-2021-47656 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (17th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-47656?
CVE-2021-47656 has a CVSS v3 base score of 7.8 (NVD).
How do I remediate CVE-2021-47656?
A fix for CVE-2021-47656 is available: update to the fixed version the vendor names in its advisory.

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