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CVE Record

CVE-2024-42256: cifs: Fix server re-repick on subrequest retry

In the Linux kernel, the following vulnerability has been resolved: cifs: Fix server re-repick on subrequest retry When a subrequest is marked for needing retry, netfs will call cifs_prepare_write() which will make cifs repick the server for the op before renegotiating credits; it then calls cifs_issue_write() which invokes smb2_async_writev() - which re-repicks the server. If a different server is then selected, this causes the increment of server->in_flight to happen against one record and the decrement to happen against another, leading to misaccounting. Fix this by just removing the repick code in smb2_async_writev(). As this is only called from netfslib-driven code, cifs_prepare_write() should always have been called first, and so server should never be NULL and the preparatory step is repeated in the event that we do a retry. The problem manifests as a warning looking something like: WARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs] ... RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs] ... smb2_writev_callback+0x334/0x560 [cifs] cifs_demultiplex_thread+0x77a/0x11b0 [cifs] kthread+0x187/0x1d0 ret_from_fork+0x34/0x60 ret_from_fork_asm+0x1a/0x30 Which may be triggered by a number of different xfstests running against an Azure server in multichannel mode. generic/249 seems the most repeatable, but generic/215, generic/249 and generic/308 may also show it.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux CIFS/SMB client accounting flaw can mishandle in-flight writes when a retried subrequest switches servers. The resulting inconsistency can trigger kernel warnings and potentially disrupt availability. Systems using affected kernels for SMB storage, particularly multichannel Azure configurations, deserve prompt review.

Executive priority

Treat as a high-priority availability issue for affected SMB-dependent systems, especially production storage clients using multichannel. Accelerate kernel validation and patching where interruption would affect critical services. Broader emergency action is not supported because active exploitation is unconfirmed.

Technical view

During a netfslib write retry, CIFS selected a server in cifs_prepare_write(), then selected again in smb2_async_writev(). If selections differed, server->in_flight was incremented and decremented on different records. The upstream resolution removes the second selection. Testing reproduced warnings during several xfstests against Azure SMB in multichannel mode.

Likely exposure

The supplied record identifies Linux 6.10 through 6.10.1 and 6.11 as affected. Practical exposure requires CIFS/SMB client write activity and the retry path; multichannel Azure testing reproduced the issue. The sources do not establish whether every listed kernel configuration is equally exposed.

Exploitation context

CVSS 3.1 rates this 7.5 for availability impact, but the supplied sources describe test-triggered kernel warnings, not a demonstrated attack. The record is not in KEV, and no cited evidence supports active exploitation, public weaponization, confidentiality loss, or data modification.

Researcher notes

The disclosed failure is cross-record in-flight accounting caused by duplicate server selection during retry handling. The supplied material demonstrates a warning under xfstests, but does not document panic frequency, denial-of-service reliability, a hostile trigger, or exact fixed release versions. Validate fixes by commit inclusion or distribution guidance.

Mitigation direction

  • Upgrade to a vendor-supported kernel release incorporating the cited upstream fix.
  • Confirm the distribution kernel package includes the applicable stable-kernel correction.
  • Review current Linux vendor guidance before applying configuration-based workarounds.
  • Prioritize SMB clients using multichannel or Azure-hosted SMB storage.

Validation and detection

  • Inventory Linux kernel versions on systems mounting CIFS or SMB shares.
  • Identify clients using SMB multichannel, especially with Azure-hosted servers.
  • Verify the installed kernel contains the applicable cited stable commit.
  • Search kernel logs for warnings originating from smb2_add_credits or smb2_writev_callback.
  • Retest representative SMB write and retry workloads after updating.
Prepared
Confidence
medium
Sources
4

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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CVE-2024-42256 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

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

1CVSS vectors
3Timeline events
1ADP providers
3Source links

SSVC decision data

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

CVSS vector scores

1 official score

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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2024-42256Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux3ee1a1fc39819906f04d6c62c180e760cd3a689d, 3ee1a1fc39819906f04d6c62c180e760cd3a689dunaffected
LinuxLinux6.10, 0, 6.10.1, 6.11affected
Weakness

CWE details

No CWE listed

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