CVE-2021-3923

Kernel stack disclosure via uncleared RDMA fields

Published Mar 27, 2023 · Updated Feb 24, 2025

Information disclosure in Linux Kernel allows local users to read kernel stack data through RDMA connection-manager commands. The ib_copy_ah_attr_to_user function clears only the reserved member instead of the entire GRH structure, so ucma_init_qp_attr copies 20 uninitialized bytes to user space when is_global is unset. Access requires a privileged local account and the rdma_cm device node; the disclosed stack data can help defeat kernel protections.

CVSS severity2.3
Low
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Linux Kernel allows local users to read kernel stack data through RDMA connection-manager commands. The ib_copy_ah_attr_to_user function clears only the reserved member instead of the entire GRH structure, so ucma_init_qp_attr copies 20 uninitialized bytes to user space when is_global is unset. Access requires a privileged local account and the rdma_cm device node; the disclosed stack data can help defeat kernel protections.

The record

CVE
CVE-2021-3923
Published
Mar 27, 2023
Updated
Feb 24, 2025
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-200
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Mar 27, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 24, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=unknown

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

The Linux Kernel Organization · Linux Kernelversion=unknown

Published CVSS scores

2.3NIST NVDCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N
2.3CISA-ADPCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N

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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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