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CVE Record

CVE-2021-47119: ext4: fix memory leak in ext4_fill_super

In the Linux kernel, the following vulnerability has been resolved: ext4: fix memory leak in ext4_fill_super Buffer head references must be released before calling kill_bdev(); otherwise the buffer head (and its page referenced by b_data) will not be freed by kill_bdev, and subsequently that bh will be leaked. If blocksizes differ, sb_set_blocksize() will kill current buffers and page cache by using kill_bdev(). And then super block will be reread again but using correct blocksize this time. sb_set_blocksize() didn't fully free superblock page and buffer head, and being busy, they were not freed and instead leaked. This can easily be reproduced by calling an infinite loop of: systemctl start <ext4_on_lvm>.mount, and systemctl stop <ext4_on_lvm>.mount ... since systemd creates a cgroup for each slice which it mounts, and the bh leak get amplified by a dying memory cgroup that also never gets freed, and memory consumption is much more easily noticed.

UnknownCVSS not scoredNot 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 memory leak. Under specific mount handling conditions, buffer references are not released, allowing memory consumption to grow. The public record describes easy reproduction through repeated ext4-on-LVM mount start and stop cycles, but it does not show remote exploitation or active abuse.

Executive priority

Treat this as a reliability and availability patch, not an emergency internet-facing incident based on current evidence. Patch affected Linux systems through normal kernel maintenance, prioritizing storage-heavy or automation-heavy hosts where repeated mounting can occur.

Technical view

The flaw is in ext4_fill_super. Buffer head references should be released before kill_bdev(); otherwise the buffer head and referenced page can leak when block sizes change and sb_set_blocksize() rereads the superblock. The issue is marked resolved in Linux stable commits.

Likely exposure

Exposure is most likely on Linux systems using affected kernels with ext4 filesystems, especially environments that repeatedly mount and unmount ext4 volumes such as ext4 on LVM under systemd. Internet-facing exposure is not indicated by the provided sources.

Exploitation context

The source describes repeated mount start and stop operations causing visible memory growth. KEV is false, and the bundle provides no evidence of active exploitation, public weaponization, remote attack paths, or privilege requirements beyond the ability to trigger relevant mount behavior.

Researcher notes

The record lacks CVSS, CWE, and detailed affected-version ranges beyond Linux kernel version indicators and stable commit references. Analysis should focus on kernel lineage, downstream backports, and whether local operational workflows can repeatedly exercise ext4 superblock mount paths.

Mitigation direction

  • Update to a kernel build containing the referenced stable fixes.
  • Use distribution vendor advisories to identify the corrected package version.
  • Prioritize systems with frequent ext4 mount and unmount activity.
  • Monitor memory pressure on affected hosts until patched.
  • Avoid unnecessary repeated mount cycling on vulnerable systems.

Validation and detection

  • Inventory Linux kernel versions across ext4-using systems.
  • Identify hosts using ext4 on LVM or automated mount workflows.
  • Confirm vendor kernel packages include the referenced ext4 fix.
  • Review monitoring for unexplained memory growth during mount operations.
  • Check CVE and vendor records for later severity updates.
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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ATT&CK lookup starting points

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CVE-2021-47119 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
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.

0CVSS vectors
3Timeline events
2ADP providers
4Source links

SSVC decision data

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

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
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxac27a0ec112a089f1a5102bc8dffc79c8c815571, ac27a0ec112a089f1a5102bc8dffc79c8c815571, ac27a0ec112a089f1a5102bc8dffc79c8c815571unaffected
LinuxLinux2.6.19, 0, 5.10.43, 5.12.10, 5.13affected
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.