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CVE Record

CVE-2025-39979: net/mlx5: fs, fix UAF in flow counter release

In the Linux kernel, the following vulnerability has been resolved: net/mlx5: fs, fix UAF in flow counter release Fix a kernel trace [1] caused by releasing an HWS action of a local flow counter in mlx5_cmd_hws_delete_fte(), where the HWS action refcount and mutex were not initialized and the counter struct could already be freed when deleting the rule. Fix it by adding the missing initializations and adding refcount for the local flow counter struct. [1] Kernel log: Call Trace: <TASK> dump_stack_lvl+0x34/0x48 mlx5_fs_put_hws_action.part.0.cold+0x21/0x94 [mlx5_core] mlx5_fc_put_hws_action+0x96/0xad [mlx5_core] mlx5_fs_destroy_fs_actions+0x8b/0x152 [mlx5_core] mlx5_cmd_hws_delete_fte+0x5a/0xa0 [mlx5_core] del_hw_fte+0x1ce/0x260 [mlx5_core] mlx5_del_flow_rules+0x12d/0x240 [mlx5_core] ? ttwu_queue_wakelist+0xf4/0x110 mlx5_ib_destroy_flow+0x103/0x1b0 [mlx5_ib] uverbs_free_flow+0x20/0x50 [ib_uverbs] destroy_hw_idr_uobject+0x1b/0x50 [ib_uverbs] uverbs_destroy_uobject+0x34/0x1a0 [ib_uverbs] uobj_destroy+0x3c/0x80 [ib_uverbs] ib_uverbs_run_method+0x23e/0x360 [ib_uverbs] ? uverbs_finalize_object+0x60/0x60 [ib_uverbs] ib_uverbs_cmd_verbs+0x14f/0x2c0 [ib_uverbs] ? do_tty_write+0x1a9/0x270 ? file_tty_write.constprop.0+0x98/0xc0 ? new_sync_write+0xfc/0x190 ib_uverbs_ioctl+0xd7/0x160 [ib_uverbs] __x64_sys_ioctl+0x87/0xc0 do_syscall_64+0x59/0x90

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A flaw in the Linux mlx5 networking driver can access a flow-counter object after it has been freed while deleting a hardware flow rule. This can crash or corrupt the kernel and could potentially compromise confidentiality, integrity, and availability. The supplied CVSS assessment requires local, low-privileged access; remotely reachable exploitation is not established.

Executive priority

Treat as a high-priority kernel update for exposed mlx5 or RDMA systems, especially shared or multi-user infrastructure. The local-access requirement reduces urgency for isolated appliances, but kernel memory corruption carries severe potential impact. Inventory first, then apply vendor-supported fixes through normal kernel maintenance and reboot procedures.

Technical view

The mlx5 flow-steering teardown path released an HWS action whose reference count and mutex were uninitialized. During mlx5_cmd_hws_delete_fte(), the associated local flow-counter structure could already be freed, causing a use-after-free. The cited Linux fixes initialize the synchronization state and add reference counting for the local counter structure.

Likely exposure

Exposure is limited to Linux systems running an affected kernel with the mlx5 driver and relevant hardware flow-steering functionality in use. The bundle identifies Linux 6.14 and entries including 6.16.10 and 6.17 as affected, but does not clearly define the complete vulnerable version range. Confirm status against the distribution or kernel vendor.

Exploitation context

The CVSS vector rates exploitation as local, low complexity, requiring low privileges and no user interaction. The source documents a kernel trace during flow destruction, not a demonstrated security exploit. CVE-2025-39979 is not listed as KEV in the supplied bundle, and no cited source establishes active exploitation.

Researcher notes

The supplied evidence establishes a lifetime-management defect in mlx5 flow-counter teardown and provides two stable-kernel fix commits. It does not establish exploitability beyond the CVSS assessment, active attacks, or the complete affected-version boundaries. Validation should focus on driver use, flow-steering exposure, backport presence, and crash telemetry without treating the recorded trace as proof of exploitation.

Mitigation direction

  • Update to a vendor-supported kernel containing one of the cited upstream stable fixes.
  • Check distribution advisories to map the ambiguous upstream version information to installed packages.
  • Prioritize mlx5 hosts offering local or shared RDMA access to less-trusted users.
  • Restrict unnecessary local access to mlx5 flow-management interfaces until remediation is complete.

Validation and detection

  • Record the running kernel version and distribution package release on each mlx5-enabled host.
  • Confirm whether mlx5_core and mlx5_ib are loaded and relevant hardware flow steering is used.
  • Verify the installed kernel includes either cited fix or the distribution's backport.
  • Review kernel logs for mlx5 flow-destruction warnings, traces, crashes, or use-after-free reports.
  • Recheck exposure after rebooting into the remediated kernel.
Prepared
Confidence
high
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

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

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CVE-2025-39979 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/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.

1CVSS vectors
3Timeline events
0ADP providers
3Source links

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
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2025-39979Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/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.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxb581f4266928d3b5d1bbe711e39623d9a1696091, b581f4266928d3b5d1bbe711e39623d9a1696091unaffected
LinuxLinux6.14, 0, 6.16.10, 6.17affected
Weakness

CWE details

No CWE listed

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