How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, 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.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

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.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

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. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

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.

Q: How do we prioritize remediation without burning out the team?

Use a 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 so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

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.

373,546

Total vulnerabilities in the database

CVE-2025-38248 — linux / linux_kernel

Use After Free

In the Linux kernel, the following vulnerability has been resolved:

bridge: mcast: Fix use-after-free during router port configuration

The bridge maintains a global list of ports behind which a multicast router resides. The list is consulted during forwarding to ensure multicast packets are forwarded to these ports even if the ports are not member in the matching MDB entry.

When per-VLAN multicast snooping is enabled, the per-port multicast context is disabled on each port and the port is removed from the global router port list:

ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1

ip link add name dummy1 up master br1 type dummy

ip link set dev dummy1 type bridge_slave mcast_router 2

$ bridge -d mdb show | grep router router ports on br1: dummy1

ip link set dev br1 type bridge mcast_vlan_snooping 1

$ bridge -d mdb show | grep router

However, the port can be re-added to the global list even when per-VLAN multicast snooping is enabled:

ip link set dev dummy1 type bridge_slave mcast_router 0

ip link set dev dummy1 type bridge_slave mcast_router 2

$ bridge -d mdb show | grep router router ports on br1: dummy1

Since commit 4b30ae9adb04 ("net: bridge: mcast: re-implement br_multicast_{enable, disable}_port functions"), when per-VLAN multicast snooping is enabled, multicast disablement on a port will disable the per-{port, VLAN} multicast contexts and not the per-port one. As a result, a port will remain in the global router port list even after it is deleted. This will lead to a use-after-free [1] when the list is traversed (when adding a new port to the list, for example):

ip link del dev dummy1

ip link add name dummy2 up master br1 type dummy

ip link set dev dummy2 type bridge_slave mcast_router 2

Similarly, stale entries can also be found in the per-VLAN router port list. When per-VLAN multicast snooping is disabled, the per-{port, VLAN} contexts are disabled on each port and the port is removed from the per-VLAN router port list:

ip link add name br1 up type bridge vlan_filtering 1 mcast_snooping 1 mcast_vlan_snooping 1

ip link add name dummy1 up master br1 type dummy

bridge vlan add vid 2 dev dummy1

bridge vlan global set vid 2 dev br1 mcast_snooping 1

bridge vlan set vid 2 dev dummy1 mcast_router 2

$ bridge vlan global show dev br1 vid 2 | grep router router ports: dummy1

ip link set dev br1 type bridge mcast_vlan_snooping 0

$ bridge vlan global show dev br1 vid 2 | grep router

However, the port can be re-added to the per-VLAN list even when per-VLAN multicast snooping is disabled:

bridge vlan set vid 2 dev dummy1 mcast_router 0

bridge vlan set vid 2 dev dummy1 mcast_router 2

$ bridge vlan global show dev br1 vid 2 | grep router router ports: dummy1

When the VLAN is deleted from the port, the per-{port, VLAN} multicast context will not be disabled since multicast snooping is not enabled on the VLAN. As a result, the port will remain in the per-VLAN router port list even after it is no longer member in the VLAN. This will lead to a use-after-free [2] when the list is traversed (when adding a new port to the list, for example):

ip link add name dummy2 up master br1 type dummy

bridge vlan add vid 2 dev dummy2

bridge vlan del vid 2 dev dummy1

bridge vlan set vid 2 dev dummy2 mcast_router 2

Fix these issues by removing the port from the relevant (global or per-VLAN) router port list in br_multicast_port_ctx_deinit(). The function is invoked during port deletion with the per-port multicast context and during VLAN deletion with the per-{port, VLAN} multicast context.

Note that deleting the multicast router timer is not enough as it only takes care of the temporary multicast router states (1 or 3) and not the permanent one (2).

[1] BUG: KASAN: slab-out-of-bounds in br_multicast_add_router.part.0+0x3f1/0x560 Write of size 8 at addr ffff888004a67328 by task ip/384 [...] Call Trace: <TASK> dump_stack ---truncated---

Published: Jul 9, 2025
Updated: Nov 20, 2025
CVE: CVE-2025-38248
Severity: High
Exploit:
CISA KEV:

CVSS v3:

Severity: High
Score: 7.8
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CWEs:

CWE-416

Affected Software
References

Software	From	Fixed in
linux / linux_kernel	5.15	6.15.5
linux / linux_kernel	6.16-rc1	6.16-rc1.x
linux / linux_kernel	6.16-rc2	6.16-rc2.x
linux / linux_kernel	6.16-rc3	6.16-rc3.x

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

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.