CVE-2026-31649 - Vulnerability Details

- net: stmmac: fix integer underflow in chain mode

Description

In the Linux kernel, the following vulnerability has been resolved:

net: stmmac: fix integer underflow in chain mode

The jumbo_frm() chain-mode implementation unconditionally computes

len = nopaged_len - bmax;

where nopaged_len = skb_headlen(skb) (linear bytes only) and bmax is
BUF_SIZE_8KiB or BUF_SIZE_2KiB. However, the caller stmmac_xmit()
decides to invoke jumbo_frm() based on skb->len (total length including
page fragments):

is_jumbo = stmmac_is_jumbo_frm(priv, skb->len, enh_desc);

When a packet has a small linear portion (nopaged_len <= bmax) but a
large total length due to page fragments (skb->len > bmax), the
subtraction wraps as an unsigned integer, producing a huge len value
(~0xFFFFxxxx). This causes the while (len != 0) loop to execute
hundreds of thousands of iterations, passing skb->data + bmax * i
pointers far beyond the skb buffer to dma_map_single(). On IOMMU-less
SoCs (the typical deployment for stmmac), this maps arbitrary kernel
memory to the DMA engine, constituting a kernel memory disclosure and
potential memory corruption from hardware.

Fix this by introducing a buf_len local variable clamped to
min(nopaged_len, bmax). Computing len = nopaged_len - buf_len is then
always safe: it is zero when the linear portion fits within a single
descriptor, causing the while (len != 0) loop to be skipped naturally,
and the fragment loop in stmmac_xmit() handles page fragments afterward.

Published: 2026-04-24

Score: 9.8 Critical

EPSS: < 1% Very Low

KEV: No

Impact:

Action:

Analysis

Impact

An integer underflow in the STMMAC network driver’s jumbo frame handling creates an enormous length value that causes the DMA engine to map memory far beyond the intended buffer. This results in a kernel memory disclosure and potentially kernel memory corruption, exposing sensitive data and jeopardizing system integrity. The flaw is related to CWE‑190 (Integer Overflow or Underflow).

Affected Systems

All Linux kernel installations that include the STMMAC driver before the patch, particularly on SoCs that lack an IOMMU. The vulnerability is present in any kernel version up to the most recent stable releases that have not yet incorporated the commit that fixes the underflow.

Risk and Exploitability

With a CVSS score of 9.8, the vulnerability is considered critical. The EPSS score is below 1 %, indicating a low current exploitation probability, but the high impact warrants prompt action. Based on the description, the likely attack vector is sending specially crafted Ethernet frames to the affected interface, allowing an attacker with network access—local or remote—to trigger the underflow and read kernel memory. The vulnerability is not listed in the CISA KEV catalog.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`286a837217204b1ef105e3a554d0757e4fdfaac1`	affected	< 513e06735f5be575b409d195822195348b164e48
`286a837217204b1ef105e3a554d0757e4fdfaac1`	affected	< 275bdf762e82082f064e60a92448fa2ac43cf95b
`286a837217204b1ef105e3a554d0757e4fdfaac1`	affected	< a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f
`286a837217204b1ef105e3a554d0757e4fdfaac1`	affected	< b7b8012193fd98236d7ae05d4b553f010a77b2ef
`286a837217204b1ef105e3a554d0757e4fdfaac1`	affected	< 2c91b39912278d0878f9ba60ba04d2518b18a08d
`286a837217204b1ef105e3a554d0757e4fdfaac1`	affected	< 6fca757c20396dc2e604dcc61922264e9e3dc803
`286a837217204b1ef105e3a554d0757e4fdfaac1`	affected	< 10d12b9240ebf96c785f0e2e4228318cd5f3a3eb
`286a837217204b1ef105e3a554d0757e4fdfaac1`	affected	< 51f4e090b9f87b40c21b6daadb5c06e6c0a07b67

Linux

affected

Version	Status	Constraints
`3.2`	affected	—
`0`	unaffected	< 3.2
`5.10.253`	unaffected	≤ 5.10.*
`5.15.203`	unaffected	≤ 5.15.*
`6.1.169`	unaffected	≤ 6.1.*
`6.6.135`	unaffected	≤ 6.6.*
`6.12.82`	unaffected	≤ 6.12.*
`6.18.23`	unaffected	≤ 6.18.*
`6.19.13`	unaffected	≤ 6.19.*
`7.0`	unaffected	≤ *

Configuration 1 [-]

OR	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel:3.2:-::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc1::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc2::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc3::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc4::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc5::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc6::::::
	cpe:2.3:o:linux:linux_kernel:7.0:rc7::::::

No data.

Vendor Product Confidence Versions

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`[286a837217204b1ef105e3a554d0757e4fdfaac1,513e06735f5be575b409d195822195348b164e48)`	affected	code_commit	—
`[286a837217204b1ef105e3a554d0757e4fdfaac1,275bdf762e82082f064e60a92448fa2ac43cf95b)`	affected	code_commit	—
`[286a837217204b1ef105e3a554d0757e4fdfaac1,a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f)`	affected	code_commit	—
`[286a837217204b1ef105e3a554d0757e4fdfaac1,b7b8012193fd98236d7ae05d4b553f010a77b2ef)`	affected	code_commit	—
`[286a837217204b1ef105e3a554d0757e4fdfaac1,2c91b39912278d087f9ba60ba04d2518b18a08d)`	affected	code_commit	—
`[286a837217204b1ef105e3a554d0757e4fdfaac1,6fca757c20396dc2e604dcc61922264e9e3dc803)`	affected	code_commit	—
`[286a837217204b1ef105e3a554d0757e4fdfaac1,10d12b9240ebf96c785f0e2e4228318cd5f3a3eb)`	affected	code_commit	—
`[286a837217204b1ef105e3a554d0757e4fdfaac1,51f4e090b9f87b40c21b6daadb5c06e6c0a07b67)`	affected	code_commit	—

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`3.2`	affected	generic	—
`[0,3.2)`	unaffected	generic	—
`[5.10.253,5.10.*]`	unaffected	generic	—
`[5.15.203,5.15.*]`	unaffected	generic	—
`[6.1.169,6.1.*]`	unaffected	generic	—
`[6.6.135,6.6.*]`	unaffected	generic	—
`[6.12.82,6.12.*]`	unaffected	generic	—
`[6.18.23,6.18.*]`	unaffected	generic	—
`[6.19.13,6.19.*]`	unaffected	generic	—
`[7.0,*]`	unaffected	generic	—

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Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

Update the Linux kernel to a version that includes the STMMAC patch (commit 10d12b9240ebf…) or apply the vendor‑supplied security update.
If a kernel upgrade is not immediately feasible, disable the affected STMMAC network driver or bring the interface down to prevent malicious packet processing until the patch is applied.
Enable an IOMMU on the platform, if supported, to restrict DMA mappings and mitigate the risk of memory disclosure.
Reboot the system after applying the patch or configuring the workaround so that the driver is reloaded with the fixed code.

Generated by OpenCVE AI on April 28, 2026 at 13:48 UTC.

Tracking

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Advisories

Source	ID	Title
Debian DLA	DLA-4561-1	linux-6.1 security update
Debian DLA	DLA-4606-1	linux security update
Debian DSA	DSA-6238-1	linux security update
Debian DSA	DSA-6243-1	linux security update

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00076.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/stable/c/10d12b9240ebf96c785f0e2e4228318cd5f3a3eb
https://git.kernel.org/stable/c/275bdf762e82082f064e60a92448fa2ac43cf95b
https://git.kernel.org/stable/c/2c91b39912278d0878f9ba60ba04d2518b18a08d
https://git.kernel.org/stable/c/513e06735f5be575b409d195822195348b164e48
https://git.kernel.org/stable/c/51f4e090b9f87b40c21b6daadb5c06e6c0a07b67
https://git.kernel.org/stable/c/6fca757c20396dc2e604dcc61922264e9e3dc803
https://git.kernel.org/stable/c/a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f
https://git.kernel.org/stable/c/b7b8012193fd98236d7ae05d4b553f010a77b2ef
https://lore.kernel.org/linux-cve-announce/2026042459-CVE-2026-31649-b45c@gregkh/T
https://nvd.nist.gov/vuln/detail/CVE-2026-31649
https://www.cve.org/CVERecord?id=CVE-2026-31649

History

Mon, 27 Apr 2026 20:15:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-190
CPEs		cpe:2.3:o:linux:linux_kernel:3.2:-:::::: cpe:2.3:o:linux:linux_kernel:7.0:rc1:::::: cpe:2.3:o:linux:linux_kernel:7.0:rc2:::::: cpe:2.3:o:linux:linux_kernel:7.0:rc3:::::: cpe:2.3:o:linux:linux_kernel:7.0:rc4:::::: cpe:2.3:o:linux:linux_kernel:7.0:rc5:::::: cpe:2.3:o:linux:linux_kernel:7.0:rc6:::::: cpe:2.3:o:linux:linux_kernel:7.0:rc7::::::

Mon, 27 Apr 2026 15:00:00 +0000

Type	Values Removed	Values Added
Metrics	cvssV3_1 `{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}`	cvssV3_1 `{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}`

Sat, 25 Apr 2026 00:15:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-191
References		https://lore.kernel.org/linux-cve-announce/2026042459-CVE-2026-31649-b45c@gregkh/T https://nvd.nist.gov/vuln/detail/CVE-2026-31649 https://www.cve.org/CVERecord?id=CVE-2026-31649
Metrics	threat_severity `None`	cvssV3_1 `{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}` threat_severity `Important`

Fri, 24 Apr 2026 15:00:00 +0000

Type	Values Removed	Values Added
Description		In the Linux kernel, the following vulnerability has been resolved: net: stmmac: fix integer underflow in chain mode The jumbo_frm() chain-mode implementation unconditionally computes len = nopaged_len - bmax; where nopaged_len = skb_headlen(skb) (linear bytes only) and bmax is BUF_SIZE_8KiB or BUF_SIZE_2KiB. However, the caller stmmac_xmit() decides to invoke jumbo_frm() based on skb->len (total length including page fragments): is_jumbo = stmmac_is_jumbo_frm(priv, skb->len, enh_desc); When a packet has a small linear portion (nopaged_len <= bmax) but a large total length due to page fragments (skb->len > bmax), the subtraction wraps as an unsigned integer, producing a huge len value (~0xFFFFxxxx). This causes the while (len != 0) loop to execute hundreds of thousands of iterations, passing skb->data + bmax * i pointers far beyond the skb buffer to dma_map_single(). On IOMMU-less SoCs (the typical deployment for stmmac), this maps arbitrary kernel memory to the DMA engine, constituting a kernel memory disclosure and potential memory corruption from hardware. Fix this by introducing a buf_len local variable clamped to min(nopaged_len, bmax). Computing len = nopaged_len - buf_len is then always safe: it is zero when the linear portion fits within a single descriptor, causing the while (len != 0) loop to be skipped naturally, and the fragment loop in stmmac_xmit() handles page fragments afterward.
Title		net: stmmac: fix integer underflow in chain mode
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/10d12b9240ebf96c785f0e2e4228318cd5f3a3eb https://git.kernel.org/stable/c/275bdf762e82082f064e60a92448fa2ac43cf95b https://git.kernel.org/stable/c/2c91b39912278d0878f9ba60ba04d2518b18a08d https://git.kernel.org/stable/c/513e06735f5be575b409d195822195348b164e48 https://git.kernel.org/stable/c/51f4e090b9f87b40c21b6daadb5c06e6c0a07b67 https://git.kernel.org/stable/c/6fca757c20396dc2e604dcc61922264e9e3dc803 https://git.kernel.org/stable/c/a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f https://git.kernel.org/stable/c/b7b8012193fd98236d7ae05d4b553f010a77b2ef

Subscriptions

Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-04-24T14:45:02.520Z

Updated: 2026-05-11T22:12:54.099Z

Reserved: 2026-03-09T15:48:24.128Z

Link: CVE-2026-31649

Vulnrichment

No data.

NVD

Status : Analyzed

Published: 2026-04-24T15:16:44.330

Modified: 2026-04-27T20:13:49.587

Link: CVE-2026-31649

Redhat

Severity : Important

Publid Date: 2026-04-24T00:00:00Z

Links: CVE-2026-31649 - Bugzilla

OpenCVE Enrichment

Updated: 2026-04-28T14:00:16Z

Weaknesses

Impact

Affected Systems

Risk and Exploitability

Tracking

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

Subscriptions

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