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CVE Record

CVE-2021-47406: ext4: add error checking to ext4_ext_replay_set_iblocks()

In the Linux kernel, the following vulnerability has been resolved: ext4: add error checking to ext4_ext_replay_set_iblocks() If the call to ext4_map_blocks() fails due to an corrupted file system, ext4_ext_replay_set_iblocks() can get stuck in an infinite loop. This could be reproduced by running generic/526 with a file system that has inline_data and fast_commit enabled. The system will repeatedly log to the console: EXT4-fs warning (device dm-3): ext4_block_to_path:105: block 1074800922 > max in inode 131076 and the stack that it gets stuck in is: ext4_block_to_path+0xe3/0x130 ext4_ind_map_blocks+0x93/0x690 ext4_map_blocks+0x100/0x660 skip_hole+0x47/0x70 ext4_ext_replay_set_iblocks+0x223/0x440 ext4_fc_replay_inode+0x29e/0x3b0 ext4_fc_replay+0x278/0x550 do_one_pass+0x646/0xc10 jbd2_journal_recover+0x14a/0x270 jbd2_journal_load+0xc4/0x150 ext4_load_journal+0x1f3/0x490 ext4_fill_super+0x22d4/0x2c00 With this patch, generic/526 still fails, but system is no longer locking up in a tight loop. It's likely the root casue is that fast_commit replay is corrupting file systems with inline_data, and we probably need to add better error handling in the fast commit replay code path beyond what is done here, which essentially just breaks the infinite loop without reporting the to the higher levels of the code.

MediumCVSS 5.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel ext4 denial-of-service issue. Under specific ext4 fast-commit replay conditions on a corrupted filesystem, the kernel can enter a tight loop and lock up, affecting availability rather than data confidentiality.

Executive priority

Treat as a targeted availability risk, not a remote compromise issue. Patch during normal kernel maintenance, but prioritize critical Linux systems where local users or corrupted ext4 media could cause service disruption.

Technical view

The flaw is in ext4_ext_replay_set_iblocks(). When ext4_map_blocks() fails during fast-commit replay, error handling was insufficient, allowing an infinite loop. The reported trigger involved ext4 filesystems with inline_data and fast_commit enabled during generic/526 testing.

Likely exposure

Exposure is most relevant to Linux systems running affected kernel versions that mount ext4 filesystems using fast_commit and inline_data. The CVE source lists Linux kernel 5.10, 5.10.71, 5.14.10, and 5.15, but affected-version formatting is incomplete.

Exploitation context

The CVSS vector is local, low complexity, and requires low privileges. The source bundle does not show CISA KEV listing or other evidence of active exploitation. The documented impact is high availability loss from kernel lockup behavior.

Researcher notes

Evidence points to a narrow ext4 fast-commit replay error-handling bug. The upstream note says the patch breaks the infinite loop, while broader fast-commit replay corruption handling may still need improvement. Affected version metadata is not fully clean.

Mitigation direction

  • Update to a vendor kernel containing the referenced upstream stable fixes.
  • Prioritize systems using ext4 with fast_commit and inline_data features.
  • Check Linux distribution advisories for exact fixed package versions.
  • Plan reboot windows where kernel updates require restart.
  • Monitor for recurring ext4_block_to_path warnings on affected hosts.

Validation and detection

  • Inventory Linux kernel versions across servers and endpoints.
  • Identify systems mounting ext4 filesystems with fast_commit and inline_data.
  • Compare installed kernels with distribution advisories and stable fix commits.
  • Review logs for repeated ext4_block_to_path warnings or mount-time recovery loops.
  • Confirm updated kernels are running after maintenance reboots.
Prepared
Confidence
medium
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2021-47406 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.5 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
2ADP providers
4Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
5.5CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H1.83.6CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

5.5Medium
CVSS 3.1 vector shape for CVE-2021-47406Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux8016e29f4362e285f0f7e38fadc61a5b7bdfdfa2, 8016e29f4362e285f0f7e38fadc61a5b7bdfdfa2, 8016e29f4362e285f0f7e38fadc61a5b7bdfdfa2unaffected
LinuxLinux5.10, 0, 5.10.71, 5.14.10, 5.15affected
Weakness

CWE details

No CWE listed

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