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Linux KernelOperating system · Linux

CVE-2021-47136

MEDIUM · 5.5 CVSS v3.1 Published 2024-03-25
Fix available
A fix is available. Upgrade to 5.10.42 / 5.12.9 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the Linux kernel, the following vulnerability has been resolved: net: zero-initialize tc skb extension on allocation Function skb_ext_add() doesn't initialize created skb extension with any value and leaves it up to the user. However, since extension of type TC_SKB_EXT originally contained only single value tc_skb_ext->chain its users used to just assign the chain value without setting whole extension memory to zero first. This assumption changed when TC_SKB_EXT extension was extended with additional fields but not all users were updated to initialize the new fields which leads to use of uninitialized memory afterwards. UBSAN log: [ 778.299821] UBSAN: invalid-load in net/openvswitch/flow.c:899:28 [ 778.301495] load of value 107 is not a valid value for type '_Bool' [ 778.303215] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.12.0-rc7+ #2 [ 778.304933] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 [ 778.307901] Call Trace: [ 778.308680] <IRQ> [ 778.309358] dump_stack+0xbb/0x107 [ 778.310307] ubsan_epilogue+0x5/0x40 [ 778.311167] __ubsan_handle_load_invalid_value.cold+0x43/0x48 [ 778.312454] ? memset+0x20/0x40 [ 778.313230] ovs_flow_key_extract.cold+0xf/0x14 [openvswitch] [ 778.314532] ovs_vport_receive+0x19e/0x2e0 [openvswitch] [ 778.315749] ? ovs_vport_find_upcall_portid+0x330/0x330 [openvswitch] [ 778.317188] ? create_prof_cpu_mask+0x20/0x20 [ 778.318220] ? arch_stack_walk+0x82/0xf0 [ 778.319153] ? secondary_startup_64_no_verify+0xb0/0xbb [ 778.320399] ? stack_trace_save+0x91/0xc0 [ 778.321362] ? stack_trace_consume_entry+0x160/0x160 [ 778.322517] ? lock_release+0x52e/0x760 [ 778.323444] netdev_frame_hook+0x323/0x610 [openvswitch] [ 778.324668] ? ovs_netdev_get_vport+0xe0/0xe0 [openvswitch] [ 778.325950] __netif_receive_skb_core+0x771/0x2db0 [ 778.327067] ? lock_downgrade+0x6e0/0x6f0 [ 778.328021] ? lock_acquire+0x565/0x720 [ 778.328940] ? generic_xdp_tx+0x4f0/0x4f0 [ 778.329902] ? inet_gro_receive+0x2a7/0x10a0 [ 778.330914] ? lock_downgrade+0x6f0/0x6f0 [ 778.331867] ? udp4_gro_receive+0x4c4/0x13e0 [ 778.332876] ? lock_release+0x52e/0x760 [ 778.333808] ? dev_gro_receive+0xcc8/0x2380 [ 778.334810] ? lock_downgrade+0x6f0/0x6f0 [ 778.335769] __netif_receive_skb_list_core+0x295/0x820 [ 778.336955] ? process_backlog+0x780/0x780 [ 778.337941] ? mlx5e_rep_tc_netdevice_event_unregister+0x20/0x20 [mlx5_core] [ 778.339613] ? seqcount_lockdep_reader_access.constprop.0+0xa7/0xc0 [ 778.341033] ? kvm_clock_get_cycles+0x14/0x20 [ 778.342072] netif_receive_skb_list_internal+0x5f5/0xcb0 [ 778.343288] ? __kasan_kmalloc+0x7a/0x90 [ 778.344234] ? mlx5e_handle_rx_cqe_mpwrq+0x9e0/0x9e0 [mlx5_core] [ 778.345676] ? mlx5e_xmit_xdp_frame_mpwqe+0x14d0/0x14d0 [mlx5_core] [ 778.347140] ? __netif_receive_skb_list_core+0x820/0x820 [ 778.348351] ? mlx5e_post_rx_mpwqes+0xa6/0x25d0 [mlx5_core] [ 778.349688] ? napi_gro_flush+0x26c/0x3c0 [ 778.350641] napi_complete_done+0x188/0x6b0 [ 778.351627] mlx5e_napi_poll+0x373/0x1b80 [mlx5_core] [ 778.352853] __napi_poll+0x9f/0x510 [ 778.353704] ? mlx5_flow_namespace_set_mode+0x260/0x260 [mlx5_core] [ 778.355158] net_rx_action+0x34c/0xa40 [ 778.356060] ? napi_threaded_poll+0x3d0/0x3d0 [ 778.357083] ? sched_clock_cpu+0x18/0x190 [ 778.358041] ? __common_interrupt+0x8e/0x1a0 [ 778.359045] __do_softirq+0x1ce/0x984 [ 778.359938] __irq_exit_rcu+0x137/0x1d0 [ 778.360865] irq_exit_rcu+0xa/0x20 [ 778.361708] common_interrupt+0x80/0xa0 [ 778.362640] </IRQ> [ 778.363212] asm_common_interrupt+0x1e/0x40 [ 778.364204] RIP: 0010:native_safe_halt+0xe/0x10 [ 778.365273] Code: 4f ff ff ff 4c 89 e7 e8 50 3f 40 fe e9 dc fe ff ff 48 89 df e8 43 3f 40 fe eb 90 cc e9 07 00 00 00 0f 00 2d 74 05 62 00 fb f4 <c3> 90 e9 07 00 00 00 0f 00 2d 64 05 62 00 f4 c3 cc cc 0f 1f 44 00 [ 778.369355] RSP: 0018:ffffffff84407e48 EFLAGS: 00000246 [ 778.370570] RAX ---truncated---

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-908

Memory or a resource is used before it has been initialised, so its contents are whatever happened to be there — sometimes leaking earlier data, sometimes values an attacker can influence. Behaviour becomes unpredictable and occasionally exploitable. Remediation is initialising every resource before use and ensuring initialisation happens on all code paths.

General guidance for the use of uninitialized resource class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 5.9, < 5.10.42>= 5.11, < 5.12.9= 5.13

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.10.42 / 5.12.9 or later
Fixed in 5.10.425.12.9
Vendor patch git.kernel.org →
Recommended fix High confidence

Linux kernel 5.10.42+, 5.12.9+, or 5.14+

  1. Upgrade the Linux kernel to version 5.10.42 or later if currently running 5.9 to 5.10.41
  2. Upgrade the Linux kernel to version 5.12.9 or later if currently running 5.11 to 5.12.8
  3. Upgrade the Linux kernel to version 5.14 or later if currently running 5.13
  4. After upgrading, verify the fix by checking that the kernel includes commit 86ab133b695ed7ba1f8786b12f4ca43137ad8c18 (net: zero-initialize tc skb extension on allocation)
Caveat Kernel upgrades may require system reboot and could introduce compatibility changes with existing drivers or modules; test in staging environment before production deployment

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-47136 in production — separate from our analysis above.

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