CVE-2021-46936— net: fix use-after-free in tw_timer_handler
Quick assessment
Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel 存在安全漏洞，该漏洞源于 tw_timer_handler 中的释放后重用。
Possible ATT&CK Techniques 1 AI
T1499.002 · Service Exhaustion FloodAffected Version Matrix 18
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| Linux | Linux | 61a7e26028b94805fd686a6dc9dbd9941f8f19b0< 15579e1301f856ad9385d720c9267c11032a5022 |
affected |
61a7e26028b94805fd686a6dc9dbd9941f8f19b0< e73164e89d1be561228a4534e1091369ee4ba41a |
affected | ||
61a7e26028b94805fd686a6dc9dbd9941f8f19b0< 5c2fe20ad37ff56070ae0acb34152333976929b4 |
affected | ||
61a7e26028b94805fd686a6dc9dbd9941f8f19b0< a8e1944b44f94f5c5f530e434c5eaee787254566 |
affected | ||
61a7e26028b94805fd686a6dc9dbd9941f8f19b0< fe5838c22b986c1190f1dce9aa09bf6a491c1a69 |
affected | ||
61a7e26028b94805fd686a6dc9dbd9941f8f19b0< 2386e81a1d277f540e1285565c9d41d531bb69d4 |
affected | ||
61a7e26028b94805fd686a6dc9dbd9941f8f19b0< 08eacbd141e2495d2fcdde84358a06c4f95cbb13 |
affected | ||
61a7e26028b94805fd686a6dc9dbd9941f8f19b0< e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0 |
affected | ||
| … +10 more rows | |||
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I. Basic Information for CVE-2021-46936
Vulnerability Information
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Vulnerability Title
net: fix use-after-free in tw_timer_handler
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved:
net: fix use-after-free in tw_timer_handler
A real world panic issue was found as follow in Linux 5.4.
BUG: unable to handle page fault for address: ffffde49a863de28
PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0
RIP: 0010:tw_timer_handler+0x20/0x40
Call Trace:
<IRQ>
call_timer_fn+0x2b/0x120
run_timer_softirq+0x1ef/0x450
__do_softirq+0x10d/0x2b8
irq_exit+0xc7/0xd0
smp_apic_timer_interrupt+0x68/0x120
apic_timer_interrupt+0xf/0x20
This issue was also reported since 2017 in the thread [1],
unfortunately, the issue was still can be reproduced after fixing
DCCP.
The ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net
namespace is destroyed since tcp_sk_ops is registered befrore
ipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops
in the list of pernet_list. There will be a use-after-free on
net->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net
if there are some inflight time-wait timers.
This bug is not introduced by commit f2bf415cfed7 ("mib: add net to
NET_ADD_STATS_BH") since the net_statistics is a global variable
instead of dynamic allocation and freeing. Actually, commit
61a7e26028b9 ("mib: put net statistics on struct net") introduces
the bug since it put net statistics on struct net and free it when
net namespace is destroyed.
Moving init_ipv4_mibs() to the front of tcp_init() to fix this bug
and replace pr_crit() with panic() since continuing is meaningless
when init_ipv4_mibs() fails.
[1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel 存在安全漏洞，该漏洞源于 tw_timer_handler 中的释放后重用。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
II. Public POCs for CVE-2021-46936
| # | POC Description | Source Link | Shenlong Link |
|---|
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Other References for CVE-2021-46936 (8)
Same Patch Batch · Linux · 2024-02-27 · 67 CVEs total
| CVE-2021-46911 | 9.8 CRITICAL | ch_ktls: Fix kernel panic |
| CVE-2021-46955 | 8.2 HIGH | openvswitch: fix stack OOB read while fragmenting IPv4 packets |
| CVE-2021-46925 | 7.8 HIGH | net/smc: fix kernel panic caused by race of smc_sock |
| CVE-2021-46963 | 7.8 HIGH | scsi: qla2xxx: Fix crash in qla2xxx_mqueuecommand() |
| CVE-2021-46929 | 7.8 HIGH | sctp: use call_rcu to free endpoint |
| CVE-2021-46913 | 7.8 HIGH | netfilter: nftables: clone set element expression template |
| CVE-2021-46973 | 7.8 HIGH | net: qrtr: Avoid potential use after free in MHI send |
| CVE-2021-46933 | 7.8 HIGH | usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear. |
| CVE-2021-46958 | 7.8 HIGH | btrfs: fix race between transaction aborts and fsyncs leading to use-after-free |
| CVE-2021-46969 | 7.8 HIGH | bus: mhi: core: Fix invalid error returning in mhi_queue |
| CVE-2021-46922 | 7.8 HIGH | KEYS: trusted: Fix TPM reservation for seal/unseal |
| CVE-2021-46967 | 7.8 HIGH | vhost-vdpa: fix vm_flags for virtqueue doorbell mapping |
| CVE-2021-46921 | 7.8 HIGH | locking/qrwlock: Fix ordering in queued_write_lock_slowpath() |
| CVE-2021-46948 | 7.5 HIGH | sfc: farch: fix TX queue lookup in TX event handling |
| CVE-2021-46960 | 7.5 HIGH | cifs: Return correct error code from smb2_get_enc_key |
| CVE-2021-46912 | 7.3 HIGH | net: Make tcp_allowed_congestion_control readonly in non-init netns |
| CVE-2021-46908 | 7.1 HIGH | bpf: Use correct permission flag for mixed signed bounds arithmetic |
| CVE-2021-46974 | 7.1 HIGH | bpf: Fix masking negation logic upon negative dst register |
| CVE-2021-46910 | 7.0 HIGH | ARM: 9063/1: mm: reduce maximum number of CPUs if DEBUG_KMAP_LOCAL is enabled |
| CVE-2021-46952 | NFS: fs_context: validate UDP retrans to prevent shift out-of-bounds |
Showing top 20 of 67 CVEs. View all on vendor page → →
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V. Comments for CVE-2021-46936
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