VulnerabilityPublished 24 Apr 2026Updated 19 Oct 2026

CVE-2026-31649: Linux kernel · net: stmmac: fix integer underflow in chain mode

Affects Linux kernelSource CVE Database V5

Not known to be exploited · CVSS 9.8 Critical · fixed in b7b8012193fd98236d7ae05d4b553f010a77b2ef : patch Linux kernel as a priority.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score

9.8Critical

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

EPSS

0.4% chance of exploitation in 30 days – higher than 39% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers can reliably automate steps 1–4 of the kill chain
Technical impact: Total control over the software or total information disclosure

CISA SSVC assessment, 2026-10-16.

Patch

Available – fixed in b7b8012193fd98236d7ae05d4b553f010a77b2ef, a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f, 513e06735f5be575b409d195822195348b164e48 +5

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
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: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
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 24 Apr 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.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 286a837217204b1ef105e3a554d0757e4fdfaac1, < b7b8012193fd98236d7ae05d4b553f010a77b2ef	Fixed in b7b8012193fd98236d7ae05d4b553f010a77b2ef
LinuxLinux	Affected ≥ 286a837217204b1ef105e3a554d0757e4fdfaac1, < a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f	Fixed in a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f
LinuxLinux	Affected ≥ 286a837217204b1ef105e3a554d0757e4fdfaac1, < 513e06735f5be575b409d195822195348b164e48	Fixed in 513e06735f5be575b409d195822195348b164e48
LinuxLinux	Affected ≥ 286a837217204b1ef105e3a554d0757e4fdfaac1, < 275bdf762e82082f064e60a92448fa2ac43cf95b	Fixed in 275bdf762e82082f064e60a92448fa2ac43cf95b
LinuxLinux	Affected ≥ 286a837217204b1ef105e3a554d0757e4fdfaac1, < 51f4e090b9f87b40c21b6daadb5c06e6c0a07b67	Fixed in 51f4e090b9f87b40c21b6daadb5c06e6c0a07b67
LinuxLinux	Affected ≥ 286a837217204b1ef105e3a554d0757e4fdfaac1, < 10d12b9240ebf96c785f0e2e4228318cd5f3a3eb	Fixed in 10d12b9240ebf96c785f0e2e4228318cd5f3a3eb

AI-suggested

A fix is available and has been applied in the Linux kernel commits identified by the fixedVersions hashes. Users and administrators should update their Linux kernel to a version including these fixes to remediate the vulnerability. No additional mitigation is required once the kernel is updated.

Description

CVE-2026-31649 is a critical integer underflow vulnerability in the stmmac network driver of the Linux kernel. The flaw occurs in the jumbo_frm() chain-mode implementation where an unsigned integer underflow causes an excessively large loop iteration count. This leads to dma_map_single() being called with pointers far beyond the intended buffer, potentially exposing kernel memory and causing memory corruption on systems without IOMMU. The issue is fixed by clamping buffer length calculations to prevent underflow and ensure safe loop execution.

Impact

This vulnerability allows an attacker to cause the kernel to map arbitrary kernel memory to the DMA engine, leading to kernel memory disclosure and potential memory corruption. The impact is critical as it affects confidentiality, integrity, and availability of the system. Exploitation does not require privileges or user interaction. The vulnerability is particularly severe on systems without IOMMU, which is common for stmmac deployments.

Summary

The Linux kernel's stmmac driver had an integer underflow in the jumbo_frm() chain-mode implementation. The function computed len = nopaged_len - bmax without validating that nopaged_len was greater than bmax. When skb->len (total packet length) was large due to page fragments but the linear portion nopaged_len was small, this subtraction wrapped around as an unsigned integer, resulting in a very large len value. Consequently, a loop iterated hundreds of thousands of times, passing out-of-bounds pointers to dma_map_single(), which on IOMMU-less SoCs allowed arbitrary kernel memory to be mapped to the DMA engine. This could lead to kernel memory disclosure and potential corruption. The fix introduced a local variable buf_len clamped to min(nopaged_len, bmax), ensuring len is zero or safe, preventing the loop from running excessively and handling fragments correctly.

CWE-190Integer Overflow or Wraparound (opens in a new tab)
Base weaknessLikelihood of exploit: Medium
The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
Requirements
Ensure that all protocols are strictly defined, such that all out-of-bounds behavior can be identified simply, and require strict conformance to the protocol.
Requirements · Language Selection
Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V5.4.3 (opens in a new tab)
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
Attack patterns
Forced Integer Overflow (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 13:43 UTC

WeaknessesCWE-190

Technical details

References

Community reviews

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