A 0-Day is a software vulnerability without an available fix, creating risk because defenders have limited time to mitigate exploitation.
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Background for this topic.
0-Day describes a software vulnerability unknown to the software maker or unpatched when first exploited. Attackers can use these flaws immediately, as no official fix or signature exists to block the exploit. Such vulnerabilities often affect widely deployed software or hardware, making them valuable for targeted attacks or widespread campaigns.
Because defenders lack patches or reliable detection signatures initially, they must rely on anomaly detection, network monitoring, and threat intelligence to identify suspicious activity linked to 0-day exploits. Rapid patching once a fix is released is critical to reduce exposure. Tracking emerging 0-day threats helps prioritize defensive measures and informs risk management decisions in environments where unpatched vulnerabilities pose significant security risks.
An unknown threat actor exploited a recently disclosed high-severity security flaw impacting Cisco Catalyst SD-WAN as a zero-day at least two months before it was publicly disclosed, according to new findings from Google-owned Mandiant
CVE-2026-20230 under exploitation, while an earlier SD-WAN 0-day looks even worse than we thought
Mandiant detailed the incident in a blog post Wednesday, but it’s unclear who was behind it or if they managed to get broad visibility into the victim’s internal traffic. The post Malicious hackers exploit Cisco zero-day for highest access level at communications service provider appeared first on CyberScoop.