How severe is CVE-2026-12539?

CVE-2026-12539 has a CVSS 4.0 base score of 5.7, rated medium severity.

Is CVE-2026-12539 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-2026-12539?

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

Does CVE-2026-12539 have an EU (EUVD) identifier?

Yes. CVE-2026-12539 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37893.

When was CVE-2026-12539 published?

CVE-2026-12539 was published on 2026-06-18 and last updated on 2026-06-30.

CVE-2026-12539

CVE-2026-12539 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-665.

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-2026-37893
Weakness: CWE-665
Published: 2026-06-18
Last modified: 2026-06-30

Description

Docker Sandboxes (sbx) blocks ICMP egress with an authorizer applied only at network-creation time, and does not re-apply it to networks rebuilt from disk when the Docker daemon restarts, so a restart-surviving sandbox forwards ICMP to arbitrary hosts. A workload inside a sandbox, which the threat model treats as untrusted, can therefore defeat the documented ICMP egress block to perform network reconnaissance and exfiltrate data over an ICMP covert channel, regardless of the configured allowlist.

Frequently asked questions

What is CVE-2026-12539?: Docker Sandboxes (sbx) blocks ICMP egress with an authorizer applied only at network-creation time, and does not re-apply it to networks rebuilt from disk when the Docker daemon restarts, so a restart-surviving sandbox forwards ICMP to arbitrary hosts. A workload inside a sandbox, which the threat model treats as untrusted, can therefore defeat the documented ICMP egress block to perform network reconnaissance and exfiltrate data over an ICMP covert channel, regardless of the configured allowlist.
How severe is CVE-2026-12539?: CVE-2026-12539 has a CVSS 4.0 base score of 5.7, rated medium severity.
Is CVE-2026-12539 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-2026-12539?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-12539 have an EU (EUVD) identifier?: Yes. CVE-2026-12539 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37893.
When was CVE-2026-12539 published?: CVE-2026-12539 was published on 2026-06-18 and last updated on 2026-06-30.

References

Other CWE-665 (Improper Initialization) vulnerabilities

CVE-2021-33635 — Critical (CVSS 9.8): When malicious images are pulled by isula pull, attackers can execute arbitrary code.
CVE-2022-37128 — Critical (CVSS 9.8): In D-Link DIR-816 A2_v1.10CNB04.img the network can be initialized without authentication via /goform/wizard_end.
CVE-2021-41264 — Critical (CVSS 9.8): OpenZeppelin Contracts is a library for smart contract development. In affected versions upgradeable contracts using…
CVE-2019-10196 — Critical (CVSS 9.8): A flaw was found in http-proxy-agent, prior to version 2.1.0. It was discovered http-proxy-agent passes an auth option…
CVE-2015-8367 — Critical (CVSS 9.8): The phase_one_correct function in Libraw before 0.17.1 allows attackers to cause memory errors and possibly execute…
CVE-2019-14271 — Critical (CVSS 9.8): In Docker 19.03.x before 19.03.1 linked against the GNU C Library (aka glibc), code injection can occur when the…

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