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NVD / CVE Program· CNA Linux

CVE-2025-21673: smb: client: fix double free of TCP_Server_Info::hostname

Noroxi assessment

Priority: Monitor (action score 22/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.42% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 1ea68070338518a1d31ce71e6abfe1b30001b27a, 35455f6c9326a8d10e91f3d5ba9260ab795b7d9a, 5.15; azl3 kernel 6.6.64.2-9 on Azure Linux 3.0 6.6.76.1-1; azl3 kernel 6.6.76.1-1 on Azure Linux 3.0 6.6.76.1-1.
  • Severity is disputed: the assigning authority (CNA) scores it 9.8, NVD 5.5.

Low priority for now. Upgrade to Linux Linux 1ea68070338518a1d31ce71e6abfe1b30001b27a, 35455f6c9326a8d10e91f3d5ba9260ab795b7d9a, 5.15; azl3 kernel 6.6.64.2-9 on Azure Linux 3.0 6.6.76.1-1; azl3 kernel 6.6.76.1-1 on Azure Linux 3.0 6.6.76.1-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: smb: client: fix double free of TCP_Server_Info::hostname When shutting down the server in cifs_put_tcp_session(), cifsd thread might be reconnecting to multiple DFS targets before it realizes it should exit the loop, so @server->hostname can't be freed as long as cifsd thread isn't done. Otherwise the following can happen: RIP: 0010:__slab_free+0x223/0x3c0 Code: 5e 41 5f c3 cc cc cc cc 4c 89 de 4c 89 cf 44 89 44 24 08 4c 89 1c 24 e8 fb cf 8e 00 44 8b 44 24 08 4c 8b 1c 24 e9 5f fe ff ff <0f> 0b 41 f7 45 08 00 0d 21 00 0f 85 2d ff ff ff e9 1f ff ff ff 80 RSP: 0018:ffffb26180dbfd08 EFLAGS: 00010246 RAX: ffff8ea34728e510 RBX: ffff8ea34728e500 RCX: 0000000000800068 RDX: 0000000000800068 RSI: 0000000000000000 RDI: ffff8ea340042400 RBP: ffffe112041ca380 R08: 0000000000000001 R09: 0000000000000000 R10: 6170732e31303000 R11: 70726f632e786563 R12: ffff8ea34728e500 R13: ffff8ea340042400 R14: ffff8ea34728e500 R15: 0000000000800068 FS: 0000000000000000(0000) GS:ffff8ea66fd80000(0000) 000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007ffc25376080 CR3: 000000012a2ba001 CR4: PKRU: 55555554 Call Trace: <TASK> ? show_trace_log_lvl+0x1c4/0x2df ? show_trace_log_lvl+0x1c4/0x2df ? __reconnect_target_unlocked+0x3e/0x160 [cifs] ? __die_body.cold+0x8/0xd ? die+0x2b/0x50 ? do_trap+0xce/0x120 ? __slab_free+0x223/0x3c0 ? do_error_trap+0x65/0x80 ? __slab_free+0x223/0x3c0 ? exc_invalid_op+0x4e/0x70 ? __slab_free+0x223/0x3c0 ? asm_exc_invalid_op+0x16/0x20 ? __slab_free+0x223/0x3c0 ? extract_hostname+0x5c/0xa0 [cifs] ? extract_hostname+0x5c/0xa0 [cifs] ? __kmalloc+0x4b/0x140 __reconnect_target_unlocked+0x3e/0x160 [cifs] reconnect_dfs_server+0x145/0x430 [cifs] cifs_handle_standard+0x1ad/0x1d0 [cifs] cifs_demultiplex_thread+0x592/0x730 [cifs] ? __pfx_cifs_demultiplex_thread+0x10/0x10 [cifs] kthread+0xdd/0x100 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x29/0x50 </TASK>

MediumCVSS 5.5 · v3.1—No exploit Fix available
Published
Jan 31, 2025
Updated
Oct 30, 2026
EPSS
0.4% · 36th percentile

Report tools

JSON

Action score

22

Monitor

Low priority for now.

CVSS
22 / 40 · 5.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.4%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
5.5
CNA · Linux
9.8
4.3 point gap

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2025-21673

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel5.14.19 and later · before 5.15
  • linux linux kernel5.15.3 and later · before 6.6.74
  • linux linux kernel6.7 and later · before 6.12.11
  • linux linux kernel6.13

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 49f933bb3016269dc50074eac5f6033d127644f1, 1c35a216ef77db708178ca225d796271f2f60a7a, 5.16affected
    • 7be3248f313930ff3d3436d4e9ddbe9fccc1f541 and later · before 35455f6c9326a8d10e91f3d5ba9260ab795b7d9aaffected · git
    • 7be3248f313930ff3d3436d4e9ddbe9fccc1f541 and later · before 1ea68070338518a1d31ce71e6abfe1b30001b27aaffected · git
    • 7be3248f313930ff3d3436d4e9ddbe9fccc1f541 and later · before a2be5f2ba34d0c6d5ef2624b24e3d852561fcd6aaffected · git
    • 7be3248f313930ff3d3436d4e9ddbe9fccc1f541 and later · before fa2f9906a7b333ba757a7dbae0713d8a5396186eaffected · git
    • 5.14.19 and later · before 5.15affected · semver
    • 5.15.3 and later · before 5.16affected · semver
    • before 5.16not affected · semver
    • 6.1.191 and later · up to and including 6.1.*not affected · semver
    • 6.6.74 and later · up to and including 6.6.*not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxfrom 0—
Debian:13linuxbefore 6.12.11-16.12.11-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2025-21683Jan 31, 2025 · bpf: Fix bpf_sk_select_reuseport() memory leak
    22Monitor
  • ← EarlierCVE-2024-57948Jan 31, 2025 · mac802154: check local interfaces before deleting sdata list
    22Monitor
  • Later →CVE-2025-21676Jan 31, 2025 · net: fec: handle page_pool_dev_alloc_pages error
    22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux1ea68070338518a1d31ce71e6abfe1b30001b27aVendor (CNA)
Linux Linux35455f6c9326a8d10e91f3d5ba9260ab795b7d9aVendor (CNA)
Linux Linux5.15Vendor (CNA)
Linux Linux5.16Vendor (CNA)
Linux Linuxa2be5f2ba34d0c6d5ef2624b24e3d852561fcd6aVendor (CNA)
Linux Linuxfa2f9906a7b333ba757a7dbae0713d8a5396186eVendor (CNA)
azl3 kernel 6.6.64.2-9 on Azure Linux 3.06.6.76.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
azl3 kernel 6.6.76.1-1 on Azure Linux 3.06.6.76.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
debian:linux6.12.11-1 · Debian:13Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-31608448 days apartsmb: server: avoid double-free in smb_direct_free_sendmsg after smb_direct_flush_send_list()
    39Monitor
  • CVE-2026-31609448 days apartsmb: client: avoid double-free in smbd_free_send_io() after smbd_send_batch_flush()
    39Monitor
  • CVE-2026-43011455 days apartnet/x25: Fix potential double free of skb
    39Monitor
  • CVE-2026-43414462 days apartscsi: qla2xxx: Completely fix fcport double free
    39Monitor
  • CVE-2026-52993509 days aparttipc: fix double-free in tipc_buf_append()
    39Monitor
  • CVE-2026-63888534 days apartscsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()
    39Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-415 · Double Free

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (3 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records