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NVD / CVE Program· CNA Linux

CVE-2025-21857: net/sched: cls_api: fix error handling causing NULL dereference

MediumCVSS 5.5 · v3.1—No exploit Fix available

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: 0.21% (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 071ed42cff4fcdd89025d966d48eabef59913bf2, 3c74b5787caf59bb1e9c5fe0a360643a71eb1e8a, 3e4c56cf41876ef2a82f0877fe2a67648f8632b8; azl3 kernel 6.6.78.1-3 on Azure Linux 3.0 6.6.82.1-1; azl3 kernel 6.6.82.1-1 on Azure Linux 3.0 6.6.82.1-1.

Low priority for now. Upgrade to Linux Linux 071ed42cff4fcdd89025d966d48eabef59913bf2, 3c74b5787caf59bb1e9c5fe0a360643a71eb1e8a, 3e4c56cf41876ef2a82f0877fe2a67648f8632b8; azl3 kernel 6.6.78.1-3 on Azure Linux 3.0 6.6.82.1-1; azl3 kernel 6.6.82.1-1 on Azure Linux 3.0 6.6.82.1-1 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: net/sched: cls_api: fix error handling causing NULL dereference tcf_exts_miss_cookie_base_alloc() calls xa_alloc_cyclic() which can return 1 if the allocation succeeded after wrapping. This was treated as an error, with value 1 returned to caller tcf_exts_init_ex() which sets exts->actions to NULL and returns 1 to caller fl_change(). fl_change() treats err == 1 as success, calling tcf_exts_validate_ex() which calls tcf_action_init() with exts->actions as argument, where it is dereferenced. Example trace: BUG: kernel NULL pointer dereference, address: 0000000000000000 CPU: 114 PID: 16151 Comm: handler114 Kdump: loaded Not tainted 5.14.0-503.16.1.el9_5.x86_64 #1 RIP: 0010:tcf_action_init+0x1f8/0x2c0 Call Trace: tcf_action_init+0x1f8/0x2c0 tcf_exts_validate_ex+0x175/0x190 fl_change+0x537/0x1120 [cls_flower]

Published
Mar 12, 2025
Updated
Jun 17, 2026
EPSS
0.2% · 12th 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 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

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.

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When you'll hear from us

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  • when exploit code appears or is weaponized
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  • 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

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

    • 6.3affected
    • 80cd22c35c9001fe72bf614d29439de41933deca and later · before de4b679aa3b4da7ec34f639df068b914f20e3c3caffected · git
    • 80cd22c35c9001fe72bf614d29439de41933deca and later · before 3e4c56cf41876ef2a82f0877fe2a67648f8632b8affected · git
    • 80cd22c35c9001fe72bf614d29439de41933deca and later · before 3c74b5787caf59bb1e9c5fe0a360643a71eb1e8aaffected · git
    • 80cd22c35c9001fe72bf614d29439de41933deca and later · before 071ed42cff4fcdd89025d966d48eabef59913bf2affected · git
    • before 6.3not affected · semver
    • 6.6.80 and later · up to and including 6.6.*not affected · semver
    • 6.12.17 and later · up to and including 6.12.*not affected · semver
    • 6.13.5 and later · up to and including 6.13.*not affected · semver
    • 6.14 and laternot affected · original_commit_for_fix
Affected versions · NVD (4)

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

  • linux linux kernel6.3 and later · before 6.6.80
  • linux linux kernel6.7 and later · before 6.12.17
  • linux linux kernel6.13 and later · before 6.13.5
  • linux linux kernel6.14

Package-level exposure

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

EcosystemPackageAffected rangeFix
Debian:13linuxbefore 6.12.17-16.12.17-1

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-2025-21855Mar 12, 2025 · ibmvnic: Don't reference skb after sending to VIOS
    31Monitor
  • ← EarlierCVE-2025-21856Mar 12, 2025 · s390/ism: add release function for struct device
    31Monitor
  • Later →CVE-2025-21860Mar 12, 2025 · mm/zswap: fix inconsistency when zswap_store_page() fails
    13Monitor

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 Linux071ed42cff4fcdd89025d966d48eabef59913bf2Vendor (CNA)
Linux Linux3c74b5787caf59bb1e9c5fe0a360643a71eb1e8aVendor (CNA)
Linux Linux3e4c56cf41876ef2a82f0877fe2a67648f8632b8Vendor (CNA)
Linux Linuxde4b679aa3b4da7ec34f639df068b914f20e3c3cVendor (CNA)
azl3 kernel 6.6.78.1-3 on Azure Linux 3.06.6.82.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
azl3 kernel 6.6.82.1-1 on Azure Linux 3.06.6.82.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
debian:linux6.12.17-1 · 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.

Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

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-476 · NULL Pointer Dereference

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.

References

Show all references (3 more)

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

All records