CVE-2025-21927
Description
An unchecked buffer bounds flaw was found in the Linux kernel's NVMe TCP Fabrics driver. An attacker with the ability to send a crafted packet to an affected NVMe host could exploit this flaw to alter kernel memory, leading to an escalation of privileges or a compromise of system integrity or stability.
Statement
This flaw results from an improper bounds check, which an attacker could exploit by sending a packet with a too-large header. The driver processing that header will then both read beyond the bounds of the buffer it has allocated, and will also alter memory outside of the buffer when it writes the result of digest calculations. An attacker could thus read otherwise inaccessible kernel memory, causing a denial of service or exfiltrating sensitive data, or write out of bounds, which could lead to an escalation of privileges. While NVMe over fabric is typically used in the context of a single system, Red Hat's assessment suggests an Attack Vector of Adjacent. This is due to the possibility of NVMe being used as a storage solution for a cluster or datacenter. The NVMe/TCP driver in RHEL 8 was released as a Technology Preview feature and was never considered stable or fully supported. Therefore, RHEL 8 is out of support scope for this CVE.
Mitigation
To mitigate this issue, prevent the `nvme_tcp` module from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically. Note that this will make NVMe over TCP fabrics unavailable, and as such is not a suitable mitigation for systems relying on that technology.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8 | 7.8 | 9.8 |
| Attack Vector | Adjacent Network | Local | Network |
| Attack Complexity | Low | Low | Low |
| Privileges Required | Low | Low | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | High | High | High |
| Integrity Impact | High | High | High |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands; Modify Memory
If the memory accessible by the attacker can be effectively controlled, it may be possible to execute arbitrary code, as with a standard buffer overflow. If the attacker can overwrite a pointer's worth of memory (usually 32 or 64 bits), they can alter the intended control flow by redirecting a function pointer to their own malicious code. Even when the attacker can only modify a single byte arbitrary code execution can be possible. Sometimes this is because the same problem can be exploited repeatedly to the same effect. Other times it is because the attacker can overwrite security-critical application-specific data -- such as a flag indicating whether the user is an administrator.
Availability,Confidentiality
Technical Impact: Read Memory; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)
Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
Confidentiality
Technical Impact: Read Memory
In the case of an out-of-bounds read, the attacker may have access to sensitive information. If the sensitive information contains system details, such as the current buffer's position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.
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