CVE-2021-43389

System crash via unattached CAPI controller index

Published Nov 4, 2021 · Updated Aug 4, 2024

Out-of-bounds read in the Linux kernel before 5.14.15 allows local users to crash the system through an ISDN CAPI race. The CMTPCONNADD path starts a CMTP session thread before its controller is attached, so detach_capi_ctr uses controller number -1 to index the capi_cards array. Triggering the fault requires CAP_NET_ADMIN in the initial namespace, and the grounded impact is a kernel crash rather than data disclosure or modification.

CVSS severity5.5
Medium
EPSS probability0.72%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in the Linux kernel before 5.14.15 allows local users to crash the system through an ISDN CAPI race. The CMTPCONNADD path starts a CMTP session thread before its controller is attached, so detach_capi_ctr uses controller number -1 to index the capi_cards array. Triggering the fault requires CAP_NET_ADMIN in the initial namespace, and the grounded impact is a kernel crash rather than data disclosure or modification.

The record

CVE
CVE-2021-43389
Published
Nov 4, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-125, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Nov 4, 2021CVE 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

5.5UbuntuCVSS: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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-125Out-of-bounds Read
T1499.004Application or System Exploitation

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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