# CVE-2021-47540: mt76: mt7915: fix NULL pointer dereference in mt7915_get_phy_mode > A NULL pointer dereference in the mt7915 Wi-Fi driver allows local attackers to cause a system crash by adding an IBSS interface. - **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Local or same network only - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 24 May 2024 - **Updated:** 11 May 2026 - **Also known as:** DEBIAN-CVE-2021-47540, UBUNTU-CVE-2021-47540 ## What is CVE-2021-47540? CVE-2021-47540 is a medium-severity vulnerability in Linux kernel, published on 24 May 2024. It can only be exploited from the same machine or local network, with no action from the victim. ### Official description 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) Weakness: CWE-476 (NULL Pointer Dereference) ## Which versions are affected by CVE-2021-47540? It affects 1 product. Products: Linux kernel. ## How do I fix CVE-2021-47540? Apply the vendor's patch. ## Is CVE-2021-47540 being exploited? There is no known exploitation of CVE-2021-47540 in the wild and no public exploit code. ## Other vulnerabilities in Linux kernel - [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild) - [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild) - [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild) - [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild) - [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2021-47540 and fix it if it is affected. What it is: CVE-2021-47540 is a medium-severity vulnerability in Linux kernel, published on 24 May 2024. It can only be exploited from the same machine or local network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2021-47540 in the wild and no public exploit code. Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2021-47540/ (Markdown: https://insights.sbomify.com/CVE-2021-47540/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47540 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47540 - OSV: https://osv.dev/vulnerability/CVE-2021-47540 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-47540/ Summaries are generated and may contain mistakes; the official description above is the record.