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.
WhatsApp has patched a security vulnerability in its iOS and macOS messaging clients that was exploited in targeted zero-day attacks. [...]
The Sangoma FreePBX Security Team is warning about an actively exploited FreePBX zero-day vulnerability that impacts systems with the Administrator Control Panel (ACP) is exposed to the internet. [...]
Citrix fixed three NetScaler ADC and NetScaler Gateway flaws today, including a critical remote code execution flaw tracked as CVE-2025-7775 that was actively exploited in attacks as a zero-day vulnerability. [...]