CVE-2021-3499Network attack vector

Firewall rule bypass via EgressDNS deadlock

Published Jun 2, 2021 · Updated Aug 3, 2024

Incorrect authorization in Red Hat OVN-Kubernetes 0.3.0 and earlier allows remote attackers to bypass intended egress firewall rules. The EgressDNS Add path holds e.lock while writing to a blocking channel, while updateEntryForName waits for the same lock, producing a deadlock. Adding roughly five DNS-name rules can trigger the deadlock; only clusters using the OVN-Kubernetes CNI with multiple DNS rules are exposed.

CVSS severity5.6
Medium
EPSS probability0.80%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect authorization in Red Hat OVN-Kubernetes 0.3.0 and earlier allows remote attackers to bypass intended egress firewall rules. The EgressDNS Add path holds e.lock while writing to a blocking channel, while updateEntryForName waits for the same lock, producing a deadlock. Adding roughly five DNS-name rules can trigger the deadlock; only clusters using the OVN-Kubernetes CNI with multiple DNS rules are exposed.

The record

CVE
CVE-2021-3499
Published
Jun 2, 2021
Updated
Aug 3, 2024
Vendor
Red Hat
Product
OVN-Kubernetes
Classifications
CWE-863, T1562.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 2, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=All ovn-kubernetes versions up to and including 0.3.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Red Hat · OVN-Kubernetesversion=All ovn-kubernetes versions up to and including 0.3.0

Published CVSS scores

5.6NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
6.8NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

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

Weakness, pattern, technique

CWE-863Incorrect Authorization
T1562.004Impair Defenses: Disable or Modify System Firewall

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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