Summary
In the Linux kernel, the following vulnerability has been resolved: sched: sch_cake: add bounds...
In the Linux kernel, the following vulnerability has been resolved:
sched: sch_cake: add bounds checks to host bulk flow fairness counts
Even though we fixed a logic error in the commit cited below, syzbot
still managed to trigger an underflow of the per-host bulk flow
counters, leading to an out of bounds memory access.
To avoid any such logic errors causing out of bounds memory accesses,
this commit factors out all accesses to the per-host bulk flow counters
to a series of helpers that perform bounds-checking before any
increments and decrements. This also has the benefit of improving
readability by moving the conditional checks for the flow mode into
these helpers, instead of having them spread out throughout the
code (which was the cause of the original logic error).
As part of this change, the flow quantum calculation is consolidated
into a helper function, which means that the dithering applied to the
ost load scaling is now applied both in the DRR rotation and when a
sparse flow's quantum is first initiated. The only user-visible effect
of this is that the maximum packet size that can be sent while a flow
stays sparse will now vary with +/- one byte in some cases. This should
not make a noticeable difference in practice, and thus it's not worth
complicating the code to preserve the old behaviour.
Impact
A read operation accesses a memory location beyond the intended buffer boundary. Typical impact: sensitive data disclosure or crash.
CVE-2025-21647 has a CVSS score of 7.1 (High). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2025-21647? CVE-2025-21647 is a high-severity out-of-bounds read vulnerability. No fixed version is listed yet. A read operation accesses a memory location beyond the intended buffer boundary.
- How severe is CVE-2025-21647? CVE-2025-21647 has a CVSS score of 7.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Is there a fix for CVE-2025-21647? No fixed version is listed for CVE-2025-21647 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2025-21647 exploitable, and should I be worried? Whether CVE-2025-21647 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-21647 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.