How severe is CVE-2026-12039?

CVE-2026-12039 has a CVSS 4.0 base score of 5.7, rated medium severity.

Is CVE-2026-12039 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (1st percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2026-12039?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-12039 have an EU (EUVD) identifier?

Yes. CVE-2026-12039 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37892.

When was CVE-2026-12039 published?

CVE-2026-12039 was published on 2026-06-18 and last updated on 2026-06-30.

CVE-2026-12039

CVE-2026-12039 is a medium-severity vulnerability with a CVSS 4.0 base score of 5.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-923.

Key facts

Severity: Medium (CVSS 4.0 base score 5.7)
EPSS exploit prediction: 0% (1st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-37892
Weakness: CWE-923
Published: 2026-06-18
Last modified: 2026-06-30

Description

Docker Sandboxes (sbx) enforces an HTTP/S-only egress allowlist but does not apply it to DNS resolution: the per-network embedded DNS server forwards any queried name to the host resolver whenever the network is internet-connected, without consulting the policy. A workload inside a sandbox, which the threat model treats as untrusted, can therefore encode data into DNS labels for an attacker-controlled domain and exfiltrate it through a DNS covert channel, bypassing the configured allowlist.

Frequently asked questions

What is CVE-2026-12039?: Docker Sandboxes (sbx) enforces an HTTP/S-only egress allowlist but does not apply it to DNS resolution: the per-network embedded DNS server forwards any queried name to the host resolver whenever the network is internet-connected, without consulting the policy. A workload inside a sandbox, which the threat model treats as untrusted, can therefore encode data into DNS labels for an attacker-controlled domain and exfiltrate it through a DNS covert channel, bypassing the configured allowlist.
How severe is CVE-2026-12039?: CVE-2026-12039 has a CVSS 4.0 base score of 5.7, rated medium severity.
Is CVE-2026-12039 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (1st percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-12039?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-12039 have an EU (EUVD) identifier?: Yes. CVE-2026-12039 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37892.
When was CVE-2026-12039 published?: CVE-2026-12039 was published on 2026-06-18 and last updated on 2026-06-30.

References

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