CVE-2026-31617 | usb: gadget: f_ncm: validate minimum block_len in ncm_unwrap_ntb()

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_ncm: validate minimum block_len in ncm_unwrap_ntb() The block_len read from the host-supplied NTB header is checked against ntb_max but has no lower bound. When block_len is smaller than opts->ndp_size, the bounds check of: ndp_index > (block_len - opts->ndp_size) will underflow producing a huge unsigned value that ndp_index can never exceed, defeating the check entirely. The same underflow occurs in the datagram index checks against block_len - opts->dpe_size. With those checks neutered, a malicious USB host can choose ndp_index and datagram offsets that point past the actual transfer, and the skb_put_data() copies adjacent kernel memory into the network skb. Fix this by rejecting block lengths that cannot hold at least the NTB header plus one NDP. This will make block_len - opts->ndp_size and block_len - opts->dpe_size both well-defined. Commit 8d2b1a1ec9f5 ("CDC-NCM: avoid overflow in sanity checking") fixed a related class of issues on the host side of NCM.

Published: 2026-04-24 Last update: 2026-06-29 Assigner: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-31617 is rated Low Risk (23/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.12%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-31617

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.02% 0.12% +0.11%
2 2026-04-25 — 0.02% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-31617

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.5 3.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 3.6 [email protected]
7.0 3.1 HIGH
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.0 5.9 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

Weakness enumeration for CVE-2026-31617

GitHub Security Advisory for CVE-2026-31617

GHSA-v24g-wpq8-cwqx · Severity: medium — In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_ncm: validate...

OS Trackers for CVE-2026-31617

vendor priority summary link
debian not yet assigned CVE-2026-31617 not yet assigned priority: Debian including 1 source packages (linux), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 3, open 2. https://security-tracker.debian.org/tracker/CVE-2026-31617
redhat high — https://access.redhat.com/security/cve/CVE-2026-31617
suse high CVE-2026-31617 severity important: SUSE including 18 source package names (cluster-md-kmp-default, dlm-kmp-default, …), 66 product×package rows across 16 product lines (SUSE Linux Enterprise High Availability Extension 15 SP7, SUSE Linux Enterprise Live Patching 15 SP7, … (16 product lines)): Known Not Affected 66. https://www.suse.com/security/cve/CVE-2026-31617/
ubuntu medium CVE-2026-31617 medium priority: Ubuntu including 161 source packages (linux, linux-allwinner-5.19, …), 1449 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): DNE 1048, ignored 170, needed 136, released 83, not-affected 7, needs-triage 4, pending 1. https://ubuntu.com/security/CVE-2026-31617

Affected software / configurations for CVE-2026-31617

Vendor Product Version Raw CPE
linux linux_kernel >= 5.9, < 6.6.136 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.12, < 6.12.83 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.13, < 6.18.24 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.19, < 6.19.14 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 7.0, < 7.0.1 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

References for CVE-2026-31617

URL Tags
https://git.kernel.org/stable/c/068a7f2749fff6462a0a908ec415b885fe430f50
https://git.kernel.org/stable/c/0f156bb5334e588034ca68ac2ee92b23f66e56e7 Patch
https://git.kernel.org/stable/c/1425655c2870054c3ab4712e2b6dbdd331597ada
https://git.kernel.org/stable/c/6762f8a95772265dd0c2ffe7f400493f3115b135 Patch
https://git.kernel.org/stable/c/74908b0318d1df1188457040b8714ff4d4b68126 Patch
https://git.kernel.org/stable/c/8757a2593631443648218244b9788e193ae0fdc1 Patch
https://git.kernel.org/stable/c/8b3b7bd3c02f98634baaf36c7fc7ac915f6517ca
https://git.kernel.org/stable/c/8f993d30b95dc9557a8a96ceca11abed674c8acb Patch
https://git.kernel.org/stable/c/d58ba8f6546232f8414f396c189297dbee03f1a7 Patch
https://access.redhat.com/security/cve/CVE-2026-31617
https://bugzilla.redhat.com/show_bug.cgi?id=2461448
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31617.json
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