In ISC DHCP 4.1-ESV-R1 -> 4.1-ESV-R16, ISC DHCP 4.4.0 -> 4.4.2 (Other branches of ISC DHCP (i.e., releases in the 4.0.x series or lower and releases in the 4.3.x series) are beyond their End-of-Life (EOL) and no longer supported by ISC. From inspection it is clear that the defect is also present in releases from those series, but they have not been officially tested for the vulnerability), The outcome of encountering the defect while reading a lease that will trigger it varies, according to: the component being affected (i.e., dhclient or dhcpd) whether the package was built as a 32-bit or 64-bit binary whether the compiler flag -fstack-protection-strong was used when compiling In dhclient, ISC has not successfully reproduced the error on a 64-bit system. However, on a 32-bit system it is possible to cause dhclient to crash when reading an improper lease, which could cause network connectivity problems for an affected system due to the absence of a running DHCP client process. In dhcpd, when run in DHCPv4 or DHCPv6 mode: if the dhcpd server binary was built for a 32-bit architecture AND the -fstack-protection-strong flag was specified to the compiler, dhcpd may exit while parsing a lease file containing an objectionable lease, resulting in lack of service to clients. Additionally, the offending lease and the lease immediately following it in the lease database may be improperly deleted. if the dhcpd server binary was built for a 64-bit architecture OR if the -fstack-protection-strong compiler flag was NOT specified, the crash will not occur, but it is possible for the offending lease and the lease which immediately followed it to be improperly deleted.
| Software | From | Fixed in |
|---|---|---|
| isc / dhcp | 4.1-esv-r12 | 4.1-esv-r12.x |
| isc / dhcp | 4.1-esv-r11_rc1 | 4.1-esv-r11_rc1.x |
| isc / dhcp | 4.1-esv-r11_b1 | 4.1-esv-r11_b1.x |
| isc / dhcp | 4.1-esv-r10_b1 | 4.1-esv-r10_b1.x |
| isc / dhcp | 4.1-esv-r10 | 4.1-esv-r10.x |
| isc / dhcp | 4.1-esv-r12_b1 | 4.1-esv-r12_b1.x |
| isc / dhcp | 4.1-esv-r11_rc2 | 4.1-esv-r11_rc2.x |
| isc / dhcp | 4.1-esv-r1 | 4.1-esv-r1.x |
| isc / dhcp | 4.1-esv-r10_rc1 | 4.1-esv-r10_rc1.x |
| isc / dhcp | 4.1-esv-r11 | 4.1-esv-r11.x |
| isc / dhcp | 4.1-esv-r12_p1 | 4.1-esv-r12_p1.x |
| isc / dhcp | 4.1-esv-r13 | 4.1-esv-r13.x |
| isc / dhcp | 4.1-esv-r13_b1 | 4.1-esv-r13_b1.x |
| isc / dhcp | 4.1-esv-r14 | 4.1-esv-r14.x |
| isc / dhcp | 4.1-esv-r14_b1 | 4.1-esv-r14_b1.x |
| isc / dhcp | 4.1-esv-r15 | 4.1-esv-r15.x |
| isc / dhcp | 4.1-esv-r10b1 | 4.1-esv-r10b1.x |
| isc / dhcp | 4.1-esv-r10rc1 | 4.1-esv-r10rc1.x |
| isc / dhcp | 4.1-esv-r11b1 | 4.1-esv-r11b1.x |
| isc / dhcp | 4.1-esv-r11rc1 | 4.1-esv-r11rc1.x |
| isc / dhcp | 4.1-esv-r11rc2 | 4.1-esv-r11rc2.x |
| isc / dhcp | 4.1-esv-r12-p1 | 4.1-esv-r12-p1.x |
| isc / dhcp | 4.1-esv-r12b1 | 4.1-esv-r12b1.x |
| isc / dhcp | 4.1-esv-r13b1 | 4.1-esv-r13b1.x |
| isc / dhcp | 4.1-esv-r14b1 | 4.1-esv-r14b1.x |
| isc / dhcp | 4.1-esv-r16 | 4.1-esv-r16.x |
| isc / dhcp | 4.4.0 | 4.4.2.x |
| isc / dhcp | 4.1-esv-r15-p1 | 4.1-esv-r15-p1.x |
| isc / dhcp | 4.1-esv-r15_b1 | 4.1-esv-r15_b1.x |
| fedoraproject / fedora | 33 | 33.x |
| fedoraproject / fedora | 34 | 34.x |
| debian / debian_linux | 9.0 | 9.0.x |
| siemens / ruggedcom_rox_rx1400_firmware | - | 2.15.0 |
| siemens / ruggedcom_rox_rx1500_firmware | 2.3.0 | 2.15.0 |
| siemens / ruggedcom_rox_rx1501_firmware | 2.3.0 | 2.15.0 |
| siemens / ruggedcom_rox_rx1510_firmware | 2.3.0 | 2.15.0 |
| siemens / ruggedcom_rox_rx1511_firmware | 2.3.0 | 2.15.0 |
| siemens / ruggedcom_rox_rx1512_firmware | 2.3.0 | 2.15.0 |
| siemens / ruggedcom_rox_rx1524_firmware | - | 2.15.0 |
| siemens / ruggedcom_rox_rx1536_firmware | - | 2.15.0 |
| siemens / ruggedcom_rox_rx5000_firmware | 2.3.0 | 2.15.0 |
| siemens / ruggedcom_rox_mx5000_firmware | 2.3.0 | 2.15.0 |
| siemens / sinec_ins | 1.0-sp1 | 1.0-sp1.x |
| siemens / sinec_ins | - | 1.0 |
| siemens / sinec_ins | 1.0 | 1.0.x |
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.