VulnerabilityPublished 19 Jul 2026

CVE-2026-63996: Linux kernel · ethtool: cmis: require exact CDB reply length

Source GCVE Database

Authoritative record:CVE-2026-63996· High 7.8

Not known to be exploited · CVSS 7.8 High · fixed in eb5dcd740cd7fa27bc2caeff2d28ef28e93ff4d3 : 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 eb5dcd740cd7fa27bc2caeff2d28ef28e93ff4d3, 6c3f999a9d1338c6c89a9ff4549eafe72bc2e7b1, 4d42fb88ec61f2e98c33a9e3a2de371d5edbc6b1 +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-cwvw-p4x2-27qh

What to do

Upgrade Linux kernel to eb5dcd740cd7fa27bc2caeff2d28ef28e93ff4d3, 6c3f999a9d1338c6c89a9ff4549eafe72bc2e7b1, 4d42fb88ec61f2e98c33a9e3a2de371d5edbc6b1 or 2f818cc98fd2c63a08239cb48995f6c3bfe9d9b3.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ a39c84d796254e6b1662ca0c46dbc313379e9291, < eb5dcd740cd7fa27bc2caeff2d28ef28e93ff4d3	Fixed in eb5dcd740cd7fa27bc2caeff2d28ef28e93ff4d3
LinuxLinux	Affected ≥ a39c84d796254e6b1662ca0c46dbc313379e9291, < 6c3f999a9d1338c6c89a9ff4549eafe72bc2e7b1	Fixed in 6c3f999a9d1338c6c89a9ff4549eafe72bc2e7b1
LinuxLinux	Affected ≥ a39c84d796254e6b1662ca0c46dbc313379e9291, < 4d42fb88ec61f2e98c33a9e3a2de371d5edbc6b1	Fixed in 4d42fb88ec61f2e98c33a9e3a2de371d5edbc6b1
LinuxLinux	Affected ≥ a39c84d796254e6b1662ca0c46dbc313379e9291, < 2f818cc98fd2c63a08239cb48995f6c3bfe9d9b3	Fixed in 2f818cc98fd2c63a08239cb48995f6c3bfe9d9b3
LinuxLinux	Affected =6.11	Fixed in–

AI-suggested

A fix has been implemented in the Linux kernel to require exact CDB reply lengths in the ethtool cmis driver, preventing out-of-bounds writes. Users should update their Linux kernel to a version that includes this patch. Since this is a kernel-level fix, no additional mitigation steps are required beyond applying the official kernel update. Patch status is not explicitly confirmed in the provided data; users should verify the vendor advisory or kernel changelogs for the exact fixed version.

Description

In the Linux kernel, the following vulnerability has been resolved: ethtool: cmis: require exact CDB reply length Malicious SFP module could respond with rpl_len longer than what cmis_cdb_process_reply() expected, leading to OOB writes. Malicious HW is a bit theoretical but some modules may just be buggy and/or the reads may occasionally get corrupted, so let's protect the kernel. The existing check protects from short replies. We need to protect from long ones, too. All callers that pass a non-zero rpl_exp_len cast the reply payload to a fixed-layout struct and read fields at fixed offsets, with no version negotiation or short-reply handling: - cmis_cdb_validate_password() - cmis_cdb_module_features_get() - cmis_fw_update_fw_mng_features_get() so let's assume that responses longer than expected do not have to be handled gracefully here. Add a warning message to make the debug easier in case my understanding is wrong... Note that page_data->length (argument of kmalloc) comes from last arg to ethtool_cmis_page_init() which is rpl_exp_len. Note2 that AIs also like to point out overflows in args->req.payload itself (which is a fixed-size 120 B buffer, on the stack), but callers should be reading structs defined by the standard, so protecting from requests for more data than max seem like defensive programming.

Impact

A malicious or buggy SFP module could cause out-of-bounds memory writes in the Linux kernel's ethtool cmis driver by sending longer-than-expected CDB replies. This could lead to kernel memory corruption, potentially destabilizing the system or causing undefined behavior. However, exploitation requires physical or logical access to insert or emulate a malicious SFP module, making practical exploitation less likely. No known exploits in the wild have been reported.

Summary

The Linux kernel's ethtool cmis driver previously allowed out-of-bounds writes due to insufficient validation of the length of CDB replies from SFP modules. Specifically, if a malicious or buggy SFP module responded with a reply length longer than what cmis_cdb_process_reply() expected, the kernel would cast the reply payload to fixed-layout structures without verifying the length, leading to potential memory corruption. The patch enforces exact reply length checks and adds warnings to aid debugging. This vulnerability affects kernel code that interacts with SFP modules via ethtool and is mitigated by improved defensive programming in the driver.

References

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