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CVE Record

CVE-2021-3593: An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU.

An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU. The flaw exists in the udp6_input() function and could occur while processing a udp packet that is smaller than the size of the 'udphdr' structure. This issue may lead to out-of-bounds read access or indirect host memory disclosure to the guest. The highest threat from this vulnerability is to data confidentiality. This flaw affects libslirp versions prior to 4.6.0.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This flaw can let a virtual machine guest indirectly read memory from the host process when QEMU uses SLiRP/libslirp networking. The reported impact is confidentiality, not system takeover. The main business concern is leakage across a virtualization boundary in environments running older QEMU or libslirp packages.

Executive priority

Treat as a targeted virtualization confidentiality risk. Prioritize shared, multi-tenant, lab, CI, and untrusted-guest environments first, then complete normal patch cycles for remaining QEMU hosts.

Technical view

CVE-2021-3593 is an invalid pointer initialization issue in libslirp's udp6_input() handling. A UDP packet smaller than the udphdr structure can trigger out-of-bounds read access or indirect host memory disclosure to the guest. Sources state libslirp versions before 4.6.0 are affected.

Likely exposure

Exposure is most likely in systems running QEMU with SLiRP networking backed by libslirp before 4.6.0, including distribution-packaged QEMU versions referenced by Fedora, Gentoo, Debian LTS, and NetApp advisories.

Exploitation context

The provided sources do not report active exploitation, and CISA KEV status is false. The described attack context is guest-to-host confidentiality impact through malformed network packet handling in SLiRP, but public exploit maturity is not established in the bundle.

Researcher notes

Evidence is limited to the CVE description and vendor advisories in the bundle. No CVSS vector, patch commit, or exploit confirmation is provided. Validation should focus on libslirp version, QEMU packaging, and whether SLiRP networking is reachable from untrusted guests.

Mitigation direction

  • Apply vendor QEMU or libslirp security updates for affected distributions and appliances.
  • Ensure libslirp is upgraded to 4.6.0 or later where it is separately packaged.
  • Follow Red Hat, Fedora, Gentoo, Debian, or platform vendor guidance for packaged fixes.
  • Limit untrusted guest use of SLiRP networking until affected hosts are updated.

Validation and detection

  • Inventory QEMU hosts and identify whether SLiRP or libslirp user-mode networking is in use.
  • Check installed libslirp package versions and flag versions before 4.6.0.
  • Review distribution security advisory status for Fedora, Gentoo, Debian LTS, Red Hat, and NetApp systems.
  • Confirm patched package versions are deployed through configuration management or host package records.
Prepared
Confidence
medium
Sources
9

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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CVE-2021-3593 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
0Timeline events
0ADP providers
8Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/aQEMUlibslirp 4.6.0Listed
Weakness

CWE details

CWE-824

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

CWE-824 · source CWE mapping

Access of Uninitialized Pointer

Access of Uninitialized Pointer represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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