CVE-2021-27645

Local daemon crash via stale allocation tracking

Published Feb 24, 2021 · Updated Jun 9, 2025

Double-free in GNU C Library nscd 2.29 through 2.33 allows local users to crash the daemon through an oversized netgroup response. In netgroupcache.c, addgetnetgrentX reallocates its response buffer without updating the pointer later freed during cleanup, causing the stale allocation to be freed twice. The trigger requires a local netgroup lookup whose response exceeds 1 KB; the crash redirects lookups to authentication servers and causes a performance penalty rather than a complete outage.

CVSS severity2.5
Low
EPSS probability0.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Double-free in GNU C Library nscd 2.29 through 2.33 allows local users to crash the daemon through an oversized netgroup response. In netgroupcache.c, addgetnetgrentX reallocates its response buffer without updating the pointer later freed during cleanup, causing the stale allocation to be freed twice. The trigger requires a local netgroup lookup whose response exceeds 1 KB; the crash redirects lookups to authentication servers and causes a performance penalty rather than a complete outage.

The record

CVE
CVE-2021-27645
Published
Feb 24, 2021
Updated
Jun 9, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-415, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 24, 2021CVE publishedPublication date reported by the CVE source.
  2. Jun 9, 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?

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

2.5Oracle LinuxCVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
2.5NIST NVDCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
2.5CISA-ADPCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L

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 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-415Double Free
T1499.004Application or System Exploitation

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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