VulnerabilityPublished 19 Jul 2026

CVE-2026-63995: Linux kernel · ethtool: cmis: validate start_cmd_payload_size from module

Source GCVE Database

Authoritative record:CVE-2026-63995· High 7.8

Not known to be exploited · CVSS 7.8 High · fixed in a46340da00385be7fb16c62425ebc20006f2d5d8 : patch Linux kernel soon.

Data as of 26 Oct 2026, 12:55 UTC

CVSS 3.1 base score

7.8High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 2% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in a46340da00385be7fb16c62425ebc20006f2d5d8, 0696709e951be54c699664adf546d16e28974d53, 63112b4515469d00008452d9cfe3fb3bf1aa2df3 +1

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Attack Vector: Local
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 19 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-g8c6-c8ph-pp93

What to do

Upgrade Linux kernel to a46340da00385be7fb16c62425ebc20006f2d5d8, 0696709e951be54c699664adf546d16e28974d53, 63112b4515469d00008452d9cfe3fb3bf1aa2df3 or 12c2496a71f82f63617971ca9b730dffa05cf58b.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ c4f78134d45c9619339c96b4bea380b1d0699788, < a46340da00385be7fb16c62425ebc20006f2d5d8	Fixed in a46340da00385be7fb16c62425ebc20006f2d5d8
LinuxLinux	Affected ≥ c4f78134d45c9619339c96b4bea380b1d0699788, < 0696709e951be54c699664adf546d16e28974d53	Fixed in 0696709e951be54c699664adf546d16e28974d53
LinuxLinux	Affected ≥ c4f78134d45c9619339c96b4bea380b1d0699788, < 63112b4515469d00008452d9cfe3fb3bf1aa2df3	Fixed in 63112b4515469d00008452d9cfe3fb3bf1aa2df3
LinuxLinux	Affected ≥ c4f78134d45c9619339c96b4bea380b1d0699788, < 12c2496a71f82f63617971ca9b730dffa05cf58b	Fixed in 12c2496a71f82f63617971ca9b730dffa05cf58b
LinuxLinux	Affected =6.11	Fixed in–

AI-suggested

A fix has been implemented to validate the start_cmd_payload_size and prevent out-of-bounds writes by erroring out on invalid sizes. Users should apply the official Linux kernel updates that include this patch once available. Since this is a kernel vulnerability, updating to a fixed kernel version is the recommended remediation.

Description

In the Linux kernel, the following vulnerability has been resolved: ethtool: cmis: validate start_cmd_payload_size from module The CMIS firmware update code reads start_cmd_payload_size from the module's FW Management Features CDB reply and uses it directly as the byte count for memcpy. The destination buffer is 112 bytes (ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH - 8). So a malicious module (or corrupted response) can cause a OOB write later on in cmis_fw_update_start_download(). Let's error out. If modules that expect longer LPL writes actually exist we should revisit. struct cmis_cdb_start_fw_download_pl's definition has to move, no change there.

Impact

A malicious or corrupted module can trigger an out-of-bounds write in kernel memory during the CMIS firmware update process. This could potentially lead to memory corruption, instability, or escalation of privileges within the kernel context. However, no known exploits are reported in the wild.

Summary

The Linux kernel's ethtool CMIS firmware update code reads the start_cmd_payload_size from a module's firmware management features CDB reply and uses it directly as the byte count in a memcpy operation. Since the destination buffer is limited to 112 bytes, an unchecked larger size can cause an out-of-bounds write in the cmis_fw_update_start_download() function. The fix involves validating the start_cmd_payload_size to prevent this condition and erroring out if the size is too large.

References

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