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CVE Record

CVE-2023-53667: net: cdc_ncm: Deal with too low values of dwNtbOutMaxSize

In the Linux kernel, the following vulnerability has been resolved: net: cdc_ncm: Deal with too low values of dwNtbOutMaxSize Currently in cdc_ncm_check_tx_max(), if dwNtbOutMaxSize is lower than the calculated "min" value, but greater than zero, the logic sets tx_max to dwNtbOutMaxSize. This is then used to allocate a new SKB in cdc_ncm_fill_tx_frame() where all the data is handled. For small values of dwNtbOutMaxSize the memory allocated during alloc_skb(dwNtbOutMaxSize, GFP_ATOMIC) will have the same size, due to how size is aligned at alloc time: size = SKB_DATA_ALIGN(size); size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); Thus we hit the same bug that we tried to squash with commit 2be6d4d16a084 ("net: cdc_ncm: Allow for dwNtbOutMaxSize to be unset or zero") Low values of dwNtbOutMaxSize do not cause an issue presently because at alloc_skb() time more memory (512b) is allocated than required for the SKB headers alone (320b), leaving some space (512b - 320b = 192b) for CDC data (172b). However, if more elements (for example 3 x u64 = [24b]) were added to one of the SKB header structs, say 'struct skb_shared_info', increasing its original size (320b [320b aligned]) to something larger (344b [384b aligned]), then suddenly the CDC data (172b) no longer fits in the spare SKB data area (512b - 384b = 128b). Consequently the SKB bounds checking semantics fails and panics: skbuff: skb_over_panic: text:ffffffff831f755b len:184 put:172 head:ffff88811f1c6c00 data:ffff88811f1c6c00 tail:0xb8 end:0x80 dev:<NULL> ------------[ cut here ]------------ kernel BUG at net/core/skbuff.c:113! invalid opcode: 0000 [#1] PREEMPT SMP KASAN CPU: 0 PID: 57 Comm: kworker/0:2 Not tainted 5.15.106-syzkaller-00249-g19c0ed55a470 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023 Workqueue: mld mld_ifc_work RIP: 0010:skb_panic net/core/skbuff.c:113 [inline] RIP: 0010:skb_over_panic+0x14c/0x150 net/core/skbuff.c:118 [snip] Call Trace: <TASK> skb_put+0x151/0x210 net/core/skbuff.c:2047 skb_put_zero include/linux/skbuff.h:2422 [inline] cdc_ncm_ndp16 drivers/net/usb/cdc_ncm.c:1131 [inline] cdc_ncm_fill_tx_frame+0x11ab/0x3da0 drivers/net/usb/cdc_ncm.c:1308 cdc_ncm_tx_fixup+0xa3/0x100 Deal with too low values of dwNtbOutMaxSize, clamp it in the range [USB_CDC_NCM_NTB_MIN_OUT_SIZE, CDC_NCM_NTB_MAX_SIZE_TX]. We ensure enough data space is allocated to handle CDC data by making sure dwNtbOutMaxSize is not smaller than USB_CDC_NCM_NTB_MIN_OUT_SIZE.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2023-53667 is a Linux kernel networking driver flaw that can trigger a kernel panic when the CDC NCM USB networking code accepts an output size that is too small. The documented impact is system crash or denial of service, not data theft or remote code execution.

Executive priority

Treat this as a targeted stability risk for Linux systems using CDC NCM USB networking. Prioritize normal kernel patching, with faster action for workstations, appliances, labs, or servers exposed to untrusted USB devices.

Technical view

In cdc_ncm_check_tx_max(), a positive but undersized dwNtbOutMaxSize could become tx_max. Later cdc_ncm_fill_tx_frame() allocates an SKB using that size, leaving insufficient room for CDC data after SKB metadata alignment. The fix clamps dwNtbOutMaxSize between USB_CDC_NCM_NTB_MIN_OUT_SIZE and CDC_NCM_NTB_MAX_SIZE_TX.

Likely exposure

Exposure is most relevant to Linux systems running affected kernel versions with the cdc_ncm USB networking driver reachable through CDC NCM devices or equivalent test paths. The source lists affected Linux kernel version lines but does not define distribution package status.

Exploitation context

The bundle shows no KEV listing and provides no evidence of active exploitation. The crash trace appears from syzkaller-style kernel testing. The source does not prove practical exploitation in production environments or define a remote attack path.

Researcher notes

The key condition is accepting a too-low dwNtbOutMaxSize that still becomes tx_max. The patch direction is bounds clamping, not a broader driver redesign. Public scoring, CWE mapping, and real-world exploitability are not provided in the bundle.

Mitigation direction

  • Update to a vendor kernel containing the referenced stable cdc_ncm fix.
  • Confirm distribution backports rather than relying only on upstream version numbers.
  • Disable or avoid CDC NCM USB networking where it is not operationally required.
  • Monitor Linux vendor advisories for package-specific remediation guidance.

Validation and detection

  • Inventory Linux kernel versions across systems that can use USB networking.
  • Check whether the cdc_ncm driver is present, loaded, or required.
  • Verify vendor changelogs include the stable fix or equivalent backport.
  • Review kernel logs for skb_over_panic traces involving cdc_ncm.
  • Prioritize validation on hosts accepting untrusted USB or network-adapter hardware.
Prepared
Confidence
medium
Sources
10

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
9Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux289507d3364f96f4b8814726917d572f71350d87, 289507d3364f96f4b8814726917d572f71350d87, 289507d3364f96f4b8814726917d572f71350d87, 289507d3364f96f4b8814726917d572f71350d87, 289507d3364f96f4b8814726917d572f71350d87, 289507d3364f96f4b8814726917d572f71350d87, 289507d3364f96f4b8814726917d572f71350d87, 289507d3364f96f4b8814726917d572f71350d87unaffected
LinuxLinux3.16, 0, 4.14.317, 4.19.285, 5.4.245, 5.10.181, 5.15.114, 6.1.31, 6.3.5, 6.4affected
Weakness

CWE details

No CWE listed

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