CVE-2020-12655

Filesystem sync hang via unchecked XFS free-block metadata

Published May 5, 2020 · Updated Aug 4, 2024

Infinite loop in XFS in the Linux kernel 5.6.10 and earlier allows local users to hang filesystem synchronization with crafted metadata. xfs_agf_verify accepts inconsistent AGF free-block counters, so writeback allocation repeatedly calls xfs_bmapi_write without producing an extent. Exploitation requires mounting a crafted XFS v5 image and initiating sync; affected writeback remains stuck, interrupting filesystem service.

CVSS severity5.5
Medium
EPSS probability0.45%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Infinite loop in XFS in the Linux kernel 5.6.10 and earlier allows local users to hang filesystem synchronization with crafted metadata. xfs_agf_verify accepts inconsistent AGF free-block counters, so writeback allocation repeatedly calls xfs_bmapi_write without producing an extent. Exploitation requires mounting a crafted XFS v5 image and initiating sync; affected writeback remains stuck, interrupting filesystem service.

The record

CVE
CVE-2020-12655
Published
May 5, 2020
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-835, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 5, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

2.8SUSECVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:L
2.1NVDAV:L/AC:L/Au:N/C:N/I:N/A:P
5.5NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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