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CVE-2024-35870: smb: client: fix UAF in smb2_reconnect_server()

In the Linux kernel, the following vulnerability has been resolved: smb: client: fix UAF in smb2_reconnect_server() The UAF bug is due to smb2_reconnect_server() accessing a session that is already being teared down by another thread that is executing __cifs_put_smb_ses(). This can happen when (a) the client has connection to the server but no session or (b) another thread ends up setting @ses->ses_status again to something different than SES_EXITING. To fix this, we need to make sure to unconditionally set @ses->ses_status to SES_EXITING and prevent any other threads from setting a new status while we're still tearing it down. The following can be reproduced by adding some delay to right after the ipc is freed in __cifs_put_smb_ses() - which will give smb2_reconnect_server() worker a chance to run and then accessing @ses->ipc: kinit ... mount.cifs //srv/share /mnt/1 -o sec=krb5,nohandlecache,echo_interval=10 [disconnect srv] ls /mnt/1 &>/dev/null sleep 30 kdestroy [reconnect srv] sleep 10 umount /mnt/1 ... CIFS: VFS: Verify user has a krb5 ticket and keyutils is installed CIFS: VFS: \\srv Send error in SessSetup = -126 CIFS: VFS: Verify user has a krb5 ticket and keyutils is installed CIFS: VFS: \\srv Send error in SessSetup = -126 general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b6b: 0000 [#1] PREEMPT SMP NOPTI CPU: 3 PID: 50 Comm: kworker/3:1 Not tainted 6.9.0-rc2 #1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-1.fc39 04/01/2014 Workqueue: cifsiod smb2_reconnect_server [cifs] RIP: 0010:__list_del_entry_valid_or_report+0x33/0xf0 Code: 4f 08 48 85 d2 74 42 48 85 c9 74 59 48 b8 00 01 00 00 00 00 ad de 48 39 c2 74 61 48 b8 22 01 00 00 00 00 74 69 <48> 8b 01 48 39 f8 75 7b 48 8b 72 08 48 39 c6 0f 85 88 00 00 00 b8 RSP: 0018:ffffc900001bfd70 EFLAGS: 00010a83 RAX: dead000000000122 RBX: ffff88810da53838 RCX: 6b6b6b6b6b6b6b6b RDX: 6b6b6b6b6b6b6b6b RSI: ffffffffc02f6878 RDI: ffff88810da53800 RBP: ffff88810da53800 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000001 R12: ffff88810c064000 R13: 0000000000000001 R14: ffff88810c064000 R15: ffff8881039cc000 FS: 0000000000000000(0000) GS:ffff888157c00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fe3728b1000 CR3: 000000010caa4000 CR4: 0000000000750ef0 PKRU: 55555554 Call Trace: <TASK> ? die_addr+0x36/0x90 ? exc_general_protection+0x1c1/0x3f0 ? asm_exc_general_protection+0x26/0x30 ? __list_del_entry_valid_or_report+0x33/0xf0 __cifs_put_smb_ses+0x1ae/0x500 [cifs] smb2_reconnect_server+0x4ed/0x710 [cifs] process_one_work+0x205/0x6b0 worker_thread+0x191/0x360 ? __pfx_worker_thread+0x10/0x10 kthread+0xe2/0x110 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x34/0x50 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK>

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

A race in Linux's SMB client can let one kernel worker use a session after another frees it during reconnect and teardown. The demonstrated result is a kernel general-protection fault. Systems mounting SMB/CIFS shares are the relevant population. The supplied scoring marks it critical, but the bundle does not establish active exploitation.

Executive priority

Treat this as a prompt patching priority for systems mounting SMB shares, particularly business-critical hosts exposed to connection interruptions. Accelerate normal kernel maintenance and reboot scheduling. The critical score warrants urgency, but it should not be interpreted as evidence of active attacks or demonstrated arbitrary code execution.

Technical view

CVE-2024-35870 is a CWE-416 use-after-free in smb2_reconnect_server(). Concurrent __cifs_put_smb_ses() teardown can free session IPC state while the reconnect worker accesses it. The fix makes SES_EXITING unconditional and prevents concurrent status changes during teardown. The supplied reproduction demonstrates a cifsiod kernel crash under disconnect, authentication-ticket loss, reconnect, and unmount conditions.

Likely exposure

Exposure is concentrated on Linux hosts using the kernel CIFS client to mount SMB shares. The documented trigger involves concurrent session teardown and reconnect; Kerberos-authenticated mounts appear in the reproduction. Hosts not using CIFS/SMB client functionality are unlikely to encounter this path. Exact exposure requires checking distributor backports and the referenced stable commits.

Exploitation context

The supplied bundle marks KEV false, and no cited source reports active exploitation. Evidence demonstrates a reproducible race and kernel crash, not remote compromise, privilege escalation, or data theft. Despite the supplied CVSS 9.8 rating, confidentiality and integrity consequences are not demonstrated by the provided technical description.

Researcher notes

The supplied affected-version data is ambiguous: it lists several releases without explicit range semantics and duplicates a commit identifier. Validate branch-specific fix inclusion using linked commits or distributor advisories. Concrete evidence supports a teardown/reconnect use-after-free and kernel crash; exploitability for confidentiality or integrity impact is not established.

Mitigation direction

  • Update to a vendor-supported kernel incorporating the applicable stable fix referenced by the CVE record.
  • Reboot into the updated kernel and confirm the previous kernel is no longer active.
  • Consult your Linux distributor's advisory for supported packages, backports, and interim mitigations.
  • Prioritize hosts whose SMB connections may disconnect and reconnect, especially Kerberos-authenticated mounts.

Validation and detection

  • Inventory running kernel releases and determine whether each distributor build includes a referenced stable fix.
  • Identify systems using the kernel CIFS client and active or configured SMB mounts.
  • After updating, verify the patched kernel is running and SMB mounts reconnect normally.
  • Review kernel logs for CIFS reconnect faults, general-protection faults, or cifsiod worker crashes.
Prepared
Confidence
medium
Sources
7

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-416: Exact CWE lookup

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cve · low confidence lookup

CVE-2024-35870 mapping review

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.8 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
3Timeline events
2ADP providers
6Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.8CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Linux
4.4CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N0.83.6CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

9.8Critical
CVSS 3.1 vector shape for CVE-2024-35870Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxb327a717e506980399464e304e363f94f95eb7a1, b327a717e506980399464e304e363f94f95eb7a1, b327a717e506980399464e304e363f94f95eb7a1, b327a717e506980399464e304e363f94f95eb7a1unaffected
LinuxLinux4.16, 0, 6.1.121, 6.6.29, 6.8.5, 6.9affected
Weakness

CWE details

CWE-416

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-416 · source CWE mapping

Use After Free

Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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