{"answers":{"affected":"It affects 1 product.","exploited":"There is no known exploitation of CVE-2021-46933 in the wild and no public exploit code.","fix":"Apply the vendor's patch.","what":"CVE-2021-46933 is a high-severity use after free vulnerability in Linux kernel, published on 27 Feb 2024. It can only be exploited from the same machine or local network, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2021-46933 and fix it if it is affected.\n\nWhat it is: CVE-2021-46933 is a high-severity use after free vulnerability in Linux kernel, published on 27 Feb 2024. It can only be exploited from the same machine or local network, with no action from the victim.\nExploitation: There is no known exploitation of CVE-2021-46933 in the wild and no public exploit code.\n\nAffected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.\n\nTask:\n1. 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.\n2. 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.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2021-46933/ (Markdown: https://insights.sbomify.com/CVE-2021-46933/index.md)","id":"CVE-2021-46933","markdown":"https://insights.sbomify.com/CVE-2021-46933/index.md","name":"CVE-2021-46933","record":{"aliases":["DEBIAN-CVE-2021-46933","GHSA-w6v7-mjp2-pwcf","UBUNTU-CVE-2021-46933"],"analysis":{"component_type":"kernel","fix_type":"patch","impacts":["denial_of_service","privilege_escalation"],"network_reachable":"adjacent_or_local","non_default_config":false,"product_category":"Linux kernel USB gadget","requires_auth":"low_privilege","summary":"A use-after-free vulnerability in the Linux kernel USB gadget function allows local attackers to cause a denial of service or potentially escalate privileges via refcount underflow.","user_interaction":"not_required","vuln_class":"use_after_free"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"Linux","cpe":[{"product":"linux_kernel","vendor":"linux"}],"cvss":{"score":7.8,"severity":"high","source":"cna","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"},"cwes":[{"id":"CWE-416","name":"Use After Free"},{"id":"CWE-476","name":"NULL Pointer Dereference"}],"description":"In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.\n\nffs_data_clear is indirectly called from both ffs_fs_kill_sb and\nffs_ep0_release, so it ends up being called twice when userland closes ep0\nand then unmounts f_fs.\nIf userland provided an eventfd along with function's USB descriptors, it\nends up calling eventfd_ctx_put as many times, causing a refcount\nunderflow.\nNULL-ify ffs_eventfd to prevent these extraneous eventfd_ctx_put calls.\n\nAlso, set epfiles to NULL right after de-allocating it, for readability.\n\nFor completeness, ffs_data_clear actually ends up being called thrice, the\nlast call being before the whole ffs structure gets freed, so when this\nspecific sequence happens there is a second underflow happening (but not\nbeing reported):\n\n/sys/kernel/debug/tracing# modprobe usb_f_fs\n/sys/kernel/debug/tracing# echo ffs_data_clear \u003e set_ftrace_filter\n/sys/kernel/debug/tracing# echo function \u003e current_tracer\n/sys/kernel/debug/tracing# echo 1 \u003e tracing_on\n(setup gadget, run and kill function userland process, teardown gadget)\n/sys/kernel/debug/tracing# echo 0 \u003e tracing_on\n/sys/kernel/debug/tracing# cat trace\n smartcard-openp-436     [000] .....  1946.208786: ffs_data_clear \u003c-ffs_data_closed\n smartcard-openp-431     [000] .....  1946.279147: ffs_data_clear \u003c-ffs_data_closed\n smartcard-openp-431     [000] .n...  1946.905512: ffs_data_clear \u003c-ffs_data_put\n\nWarning output corresponding to above trace:\n[ 1946.284139] WARNING: CPU: 0 PID: 431 at lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c\n[ 1946.293094] refcount_t: underflow; use-after-free.\n[ 1946.298164] Modules linked in: usb_f_ncm(E) u_ether(E) usb_f_fs(E) hci_uart(E) btqca(E) btrtl(E) btbcm(E) btintel(E) bluetooth(E) nls_ascii(E) nls_cp437(E) vfat(E) fat(E) bcm2835_v4l2(CE) bcm2835_mmal_vchiq(CE) videobuf2_vmalloc(E) videobuf2_memops(E) sha512_generic(E) videobuf2_v4l2(E) sha512_arm(E) videobuf2_common(E) videodev(E) cpufreq_dt(E) snd_bcm2835(CE) brcmfmac(E) mc(E) vc4(E) ctr(E) brcmutil(E) snd_soc_core(E) snd_pcm_dmaengine(E) drbg(E) snd_pcm(E) snd_timer(E) snd(E) soundcore(E) drm_kms_helper(E) cec(E) ansi_cprng(E) rc_core(E) syscopyarea(E) raspberrypi_cpufreq(E) sysfillrect(E) sysimgblt(E) cfg80211(E) max17040_battery(OE) raspberrypi_hwmon(E) fb_sys_fops(E) regmap_i2c(E) ecdh_generic(E) rfkill(E) ecc(E) bcm2835_rng(E) rng_core(E) vchiq(CE) leds_gpio(E) libcomposite(E) fuse(E) configfs(E) ip_tables(E) x_tables(E) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) crc32c_generic(E) sdhci_iproc(E) sdhci_pltfm(E) sdhci(E)\n[ 1946.399633] CPU: 0 PID: 431 Comm: smartcard-openp Tainted: G         C OE     5.15.0-1-rpi #1  Debian 5.15.3-1\n[ 1946.417950] Hardware name: BCM2835\n[ 1946.425442] Backtrace:\n[ 1946.432048] [\u003cc08d60a0\u003e] (dump_backtrace) from [\u003cc08d62ec\u003e] (show_stack+0x20/0x24)\n[ 1946.448226]  r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c\n[ 1946.458412] [\u003cc08d62cc\u003e] (show_stack) from [\u003cc08d9ae0\u003e] (dump_stack+0x28/0x30)\n[ 1946.470380] [\u003cc08d9ab8\u003e] (dump_stack) from [\u003cc0123500\u003e] (__warn+0xe8/0x154)\n[ 1946.482067]  r5:c04a948c r4:c0a71dc8\n[ 1946.490184] [\u003cc0123418\u003e] (__warn) from [\u003cc08d6948\u003e] (warn_slowpath_fmt+0xa0/0xe4)\n[ 1946.506758]  r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04\n[ 1946.517070] [\u003cc08d68ac\u003e] (warn_slowpath_fmt) from [\u003cc04a948c\u003e] (refcount_warn_saturate+0x110/0x15c)\n[ 1946.535309]  r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0\n[ 1946.546708] [\u003cc04a937c\u003e] (refcount_warn_saturate) from [\u003cc0380134\u003e] (eventfd_ctx_put+0x48/0x74)\n[ 1946.564476] [\u003cc03800ec\u003e] (eventfd_ctx_put) from [\u003cbf5464e8\u003e] (ffs_data_clear+0xd0/0x118 [usb_f_fs])\n[ 1946.582664]  r5:c3b84c00 r4:c2695b00\n[ 1946.590668] [\u003cbf546418\u003e] (ffs_data_clear [usb_f_fs]) from [\u003cbf547cc0\u003e] (ffs_data_closed+0x9c/0x150 [usb_f_fs])\n[ 1946.609608]  r5:bf54d014 r4:c2695b00\n[ 1946.617522] [\u003cbf547c24\u003e] (ffs_data_closed [usb_f_fs]) from [\u003cbf547da0\u003e] (ffs_fs_kill_sb+0x2c/0x30 [usb_f_fs])\n[ 1946.636217]  r7:c0dfcb\n---truncated---","ecosystems":[],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"none_known"},"has_fix":true,"headline":"usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.","id":"CVE-2021-46933","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":"linux:linux_kernel","products":["linux:linux_kernel"],"type":"use_after_free","year":"2021"},"n_packages":0,"n_references":8,"next":{"headline":"i2c: validate user data in compat ioctl","id":"CVE-2021-46934"},"packages":[],"prev":{"headline":"Input: appletouch - initialize work before device registration","id":"CVE-2021-46932"},"products":["Linux"],"published":"2024-02-27","related":[{"cvss_score":8.8,"headline":"Linux Kernel Out-of-Bounds Write","id":"CVE-2026-53266","kev_date_added":"2026-09-18","published":"2026-06-25"},{"cvss_score":8.8,"headline":"Linux Kernel Improper Input Validation","id":"CVE-2013-6282","kev_date_added":"2022-09-15","published":"2013-11-19"},{"cvss_score":8.4,"headline":"Linux Kernel Heap-Based Buffer Overflow","id":"CVE-2022-0185","kev_date_added":"2024-08-21","published":"2022-02-11"},{"cvss_score":8.4,"headline":"Linux Kernel Privilege Escalation","id":"CVE-2013-2094","kev_date_added":"2022-09-15","published":"2013-05-14"},{"cvss_score":7.8,"headline":"Linux Kernel Unspecified","id":"CVE-2026-53362","kev_date_added":"2026-08-27","published":"2026-07-04"},{"cvss_score":7.8,"headline":"Linux Kernel Missing Initialization of a Variable","id":"CVE-2026-46300","kev_date_added":"2026-10-28","published":"2026-05-23"},{"cvss_score":7.8,"headline":"Linux Kernel Race Condition","id":"CVE-2025-39964","kev_date_added":"2026-09-18","published":"2025-10-13"}],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"},{"class":"attribution","licence":"US public information, NVD API terms","name":"NVD"},{"class":"attribution","licence":"CWE Terms of Use","name":"CWE (MITRE)"},{"class":"attribution","licence":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":"no","exploitation":"none","technical_impact":"partial"},"state":"PUBLISHED","updated":"2026-08-05","vendors":["Linux"]},"summary":"A use-after-free vulnerability in the Linux kernel USB gadget function allows local attackers to cause a denial of service or potentially escalate privileges via refcount underflow.","url":"https://insights.sbomify.com/CVE-2021-46933/"}