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CVE Record

CVE-2021-47540: mt76: mt7915: fix NULL pointer dereference in mt7915_get_phy_mode

In the Linux kernel, the following vulnerability has been resolved: mt76: mt7915: fix NULL pointer dereference in mt7915_get_phy_mode Fix the following NULL pointer dereference in mt7915_get_phy_mode routine adding an ibss interface to the mt7915 driver. [ 101.137097] wlan0: Trigger new scan to find an IBSS to join [ 102.827039] wlan0: Creating new IBSS network, BSSID 26:a4:50:1a:6e:69 [ 103.064756] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 [ 103.073670] Mem abort info: [ 103.076520] ESR = 0x96000005 [ 103.079614] EC = 0x25: DABT (current EL), IL = 32 bits [ 103.084934] SET = 0, FnV = 0 [ 103.088042] EA = 0, S1PTW = 0 [ 103.091215] Data abort info: [ 103.094104] ISV = 0, ISS = 0x00000005 [ 103.098041] CM = 0, WnR = 0 [ 103.101044] user pgtable: 4k pages, 39-bit VAs, pgdp=00000000460b1000 [ 103.107565] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000, pud=0000000000000000 [ 103.116590] Internal error: Oops: 96000005 [#1] SMP [ 103.189066] CPU: 1 PID: 333 Comm: kworker/u4:3 Not tainted 5.10.75 #0 [ 103.195498] Hardware name: MediaTek MT7622 RFB1 board (DT) [ 103.201124] Workqueue: phy0 ieee80211_iface_work [mac80211] [ 103.206695] pstate: 20000005 (nzCv daif -PAN -UAO -TCO BTYPE=--) [ 103.212705] pc : mt7915_get_phy_mode+0x68/0x120 [mt7915e] [ 103.218103] lr : mt7915_mcu_add_bss_info+0x11c/0x760 [mt7915e] [ 103.223927] sp : ffffffc011cdb9e0 [ 103.227235] x29: ffffffc011cdb9e0 x28: ffffff8006563098 [ 103.232545] x27: ffffff8005f4da22 x26: ffffff800685ac40 [ 103.237855] x25: 0000000000000001 x24: 000000000000011f [ 103.243165] x23: ffffff8005f4e260 x22: ffffff8006567918 [ 103.248475] x21: ffffff8005f4df80 x20: ffffff800685ac58 [ 103.253785] x19: ffffff8006744400 x18: 0000000000000000 [ 103.259094] x17: 0000000000000000 x16: 0000000000000001 [ 103.264403] x15: 000899c3a2d9d2e4 x14: 000899bdc3c3a1c8 [ 103.269713] x13: 0000000000000000 x12: 0000000000000000 [ 103.275024] x11: ffffffc010e30c20 x10: 0000000000000000 [ 103.280333] x9 : 0000000000000050 x8 : ffffff8006567d88 [ 103.285642] x7 : ffffff8006563b5c x6 : ffffff8006563b44 [ 103.290952] x5 : 0000000000000002 x4 : 0000000000000001 [ 103.296262] x3 : 0000000000000001 x2 : 0000000000000001 [ 103.301572] x1 : 0000000000000000 x0 : 0000000000000011 [ 103.306882] Call trace: [ 103.309328] mt7915_get_phy_mode+0x68/0x120 [mt7915e] [ 103.314378] mt7915_bss_info_changed+0x198/0x200 [mt7915e] [ 103.319941] ieee80211_bss_info_change_notify+0x128/0x290 [mac80211] [ 103.326360] __ieee80211_sta_join_ibss+0x308/0x6c4 [mac80211] [ 103.332171] ieee80211_sta_create_ibss+0x8c/0x10c [mac80211] [ 103.337895] ieee80211_ibss_work+0x3dc/0x614 [mac80211] [ 103.343185] ieee80211_iface_work+0x388/0x3f0 [mac80211] [ 103.348495] process_one_work+0x288/0x690 [ 103.352499] worker_thread+0x70/0x464 [ 103.356157] kthread+0x144/0x150 [ 103.359380] ret_from_fork+0x10/0x18 [ 103.362952] Code: 394008c3 52800220 394000e4 7100007f (39400023)

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This CVE is a Linux kernel driver crash bug affecting MediaTek mt7915 Wi-Fi support. When an IBSS/ad-hoc wireless interface is added, the driver can hit a NULL pointer dereference and trigger a kernel oops. The main business impact is device instability or denial of service on systems using that wireless chipset and mode.

Executive priority

Treat this as targeted remediation, not an enterprise-wide emergency. Patch affected wireless Linux devices during the next appropriate maintenance window, faster for operationally critical appliances or products that rely on mt7915 Wi-Fi and ad-hoc networking.

Technical view

The flaw is in the mt76 mt7915 driver, specifically mt7915_get_phy_mode. The source shows a NULL pointer dereference while creating or joining an IBSS network, with the call path through mac80211 IBSS handling. Stable kernel commits are referenced as the resolution, but the bundle provides no CVSS, CWE, or exploitability assessment.

Likely exposure

Exposure is likely limited to Linux systems using MediaTek mt7915 wireless hardware and the mt76/mt7915 driver, especially where IBSS/ad-hoc mode is enabled or tested. Conventional servers, cloud workloads, and systems without this chipset or driver are unlikely to be exposed based on the provided sources.

Exploitation context

The provided sources do not report active exploitation, and KEV is false. The described trigger involves adding or creating an IBSS interface. Evidence is insufficient to claim remote unauthenticated exploitation; the supported conclusion is a driver-level crash condition under a specific wireless configuration path.

Researcher notes

The source bundle identifies the vulnerable path and stable kernel fixes but lacks CVSS, CWE, distro package mapping, and exploitability detail. Analysis should focus on driver presence, kernel lineage, and IBSS feature exposure. Do not broaden scope beyond Linux mt7915/mt76 without vendor evidence.

Mitigation direction

  • Update affected Linux kernels through vendor or distribution packages containing the referenced stable fixes.
  • Prioritize systems with MediaTek mt7915 Wi-Fi hardware and IBSS/ad-hoc mode usage.
  • If patching is delayed, avoid IBSS/ad-hoc operation on affected mt7915 devices where feasible.
  • Check Linux distribution advisories for exact fixed package versions.
  • Monitor affected devices for kernel oops events referencing mt7915_get_phy_mode.

Validation and detection

  • Inventory Linux assets for MediaTek mt7915 hardware and mt76/mt7915 driver usage.
  • Confirm running kernel versions against vendor fixed releases or the referenced stable commits.
  • Review kernel logs for NULL pointer dereference traces in mt7915_get_phy_mode.
  • Verify IBSS/ad-hoc workflows remain stable after applying the kernel update.
  • Document systems without the hardware or driver as not exposed by current evidence.
Prepared
Confidence
medium
Sources
5

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

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

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CVE-2021-47540 mapping review

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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
2ADP providers
4Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

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.

ADP provider summaries

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxe57b7901469fc0b021930b83a8094baaf3d81b09, e57b7901469fc0b021930b83a8094baaf3d81b09, e57b7901469fc0b021930b83a8094baaf3d81b09unaffected
LinuxLinux5.8, 0, 5.10.84, 5.15.7, 5.16affected
Weakness

CWE details

No CWE listed

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