How severe is CVE-2025-21857?

CVE-2025-21857 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2025-21857 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (10th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-21857?

CVE-2025-21857 primarily affects Linux Linux Kernel. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2025-21857?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2025-21857 have an EU (EUVD) identifier?

Yes. CVE-2025-21857 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-7597.

When was CVE-2025-21857 published?

CVE-2025-21857 was published on 2025-03-12 and last updated on 2026-06-17.

CVE-2025-21857

CVE-2025-21857 is a medium-severity vulnerability in Linux Linux Kernel with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-476.

Key facts

Severity: Medium (CVSS 3.x base score 5.5)
EPSS exploit prediction: 0% (10th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-7597
Weakness: CWE-476
Affected product: Linux Linux Kernel
Published: 2025-03-12
Last modified: 2026-06-17

Description

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]

Frequently asked questions

What is CVE-2025-21857?: 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]
How severe is CVE-2025-21857?: CVE-2025-21857 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2025-21857 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (10th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-21857?: CVE-2025-21857 primarily affects Linux Linux Kernel. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2025-21857?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2025-21857 have an EU (EUVD) identifier?: Yes. CVE-2025-21857 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-7597.
When was CVE-2025-21857 published?: CVE-2025-21857 was published on 2025-03-12 and last updated on 2026-06-17.

References

Affected products (4)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:6.14:rc1:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:6.14:rc2:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:6.14:rc3:*:*:*:*:*:*

More vulnerabilities in Linux Linux Kernel

CVE-2023-2163 — Critical (CVSS 10.0): Incorrect verifier pruning in BPF in Linux Kernel >=5.4 leads to unsafe code paths being incorrectly marked as safe,…
CVE-2015-8104 — Critical (CVSS 10.0): The KVM subsystem in the Linux kernel through 4.2.6, and Xen 4.3.x through 4.6.x, allows guest OS users to cause a…
CVE-2015-1421 — Critical (CVSS 10.0): Use-after-free vulnerability in the sctp_assoc_update function in net/sctp/associola.c in the Linux kernel before…
CVE-2014-2523 — Critical (CVSS 10.0): net/netfilter/nf_conntrack_proto_dccp.c in the Linux kernel through 3.13.6 uses a DCCP header pointer incorrectly,…
CVE-2010-2495 — Critical (CVSS 10.0): The pppol2tp_xmit function in drivers/net/pppol2tp.c in the L2TP implementation in the Linux kernel before 2.6.34 does…
CVE-2010-2521 — Critical (CVSS 10.0): Multiple buffer overflows in fs/nfsd/nfs4xdr.c in the XDR implementation in the NFS server in the Linux kernel before…

All CVEs affecting Linux Linux Kernel →

Other CWE-476 (NULL Pointer Dereference) vulnerabilities

CVE-2022-36648 — Critical (CVSS 10.0): The hardware emulation in the of_dpa_cmd_add_l2_flood of rocker device model in QEMU, as used in 7.0.0 and earlier,…
CVE-2020-14500 — Critical (CVSS 10.0): Secomea GateManager all versions prior to 9.2c, An attacker can send a negative value and overwrite arbitrary data.
CVE-2010-2495 — Critical (CVSS 10.0): The pppol2tp_xmit function in drivers/net/pppol2tp.c in the L2TP implementation in the Linux kernel before 2.6.34 does…
CVE-2026-46195 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: smb: client: validate dacloffset before building…
CVE-2026-31657 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: batman-adv: hold claim backbone gateways by…
CVE-2026-31436 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: dmaengine: idxd: fix possible wrong descriptor…

Browse all CWE-476 (NULL Pointer Dereference) vulnerabilities →