# CVE-2025-21868: net: allow small head cache usage with large MAX_SKB_FRAGS values
> A kernel bug in network initialization causes a warning and potential crash when using large MAX_SKB_FRAGS values, leading to denial of service.
- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Mar 2025
- **Updated:** 5 Aug 2026
- **Also known as:** AZL-62639, BELL-CVE-2025-21868, DEBIAN-CVE-2025-21868, GHSA-3w57-3p47-w8ch, ROOT-OS-UBUNTU-2404-CVE-2025-21868, UBUNTU-CVE-2025-21868
## What is CVE-2025-21868?
CVE-2025-21868 is a high-severity denial of service vulnerability in Linux kernel, published on 27 Mar 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
### Official description
In the Linux kernel, the following vulnerability has been resolved:
net: allow small head cache usage with large MAX_SKB_FRAGS values
Sabrina reported the following splat:
WARNING: CPU: 0 PID: 1 at net/core/dev.c:6935 netif_napi_add_weight_locked+0x8f2/0xba0
Modules linked in:
CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.14.0-rc1-net-00092-g011b03359038 #996
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014
RIP: 0010:netif_napi_add_weight_locked+0x8f2/0xba0
Code: e8 c3 e6 6a fe 48 83 c4 28 5b 5d 41 5c 41 5d 41 5e 41 5f c3 cc cc cc cc c7 44 24 10 ff ff ff ff e9 8f fb ff ff e8 9e e6 6a fe <0f> 0b e9 d3 fe ff ff e8 92 e6 6a fe 48 8b 04 24 be ff ff ff ff 48
RSP: 0000:ffffc9000001fc60 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff88806ce48128 RCX: 1ffff11001664b9e
RDX: ffff888008f00040 RSI: ffffffff8317ca42 RDI: ffff88800b325cb6
RBP: ffff88800b325c40 R08: 0000000000000001 R09: ffffed100167502c
R10: ffff88800b3a8163 R11: 0000000000000000 R12: ffff88800ac1c168
R13: ffff88800ac1c168 R14: ffff88800ac1c168 R15: 0000000000000007
FS: 0000000000000000(0000) GS:ffff88806ce00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff888008201000 CR3: 0000000004c94001 CR4: 0000000000370ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
gro_cells_init+0x1ba/0x270
xfrm_input_init+0x4b/0x2a0
xfrm_init+0x38/0x50
ip_rt_init+0x2d7/0x350
ip_init+0xf/0x20
inet_init+0x406/0x590
do_one_initcall+0x9d/0x2e0
do_initcalls+0x23b/0x280
kernel_init_freeable+0x445/0x490
kernel_init+0x20/0x1d0
ret_from_fork+0x46/0x80
ret_from_fork_asm+0x1a/0x30
irq event stamp: 584330
hardirqs last enabled at (584338): [] __up_console_sem+0x77/0xb0
hardirqs last disabled at (584345): [] __up_console_sem+0x5c/0xb0
softirqs last enabled at (583242): [] netlink_insert+0x14d/0x470
softirqs last disabled at (583754): [] netif_napi_add_weight_locked+0x77d/0xba0
on kernel built with MAX_SKB_FRAGS=45, where SKB_WITH_OVERHEAD(1024)
is smaller than GRO_MAX_HEAD.
Such built additionally contains the revert of the single page frag cache
so that napi_get_frags() ends up using the page frag allocator, triggering
the splat.
Note that the underlying issue is independent from the mentioned
revert; address it ensuring that the small head cache will fit either TCP
and GRO allocation and updating napi_alloc_skb() and __netdev_alloc_skb()
to select kmalloc() usage for any allocation fitting such cache.
## Which versions are affected by CVE-2025-21868?
It affects 1 product.
Products: Linux kernel.
## How do I fix CVE-2025-21868?
Apply the vendor's patch.
## Is CVE-2025-21868 being exploited?
There is no known exploitation of CVE-2025-21868 in the wild and no public exploit code.
## Other vulnerabilities in Linux kernel
- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)
## Fix prompt for AI coding agents
```text
Check this codebase for CVE-2025-21868 and fix it if it is affected.
What it is: CVE-2025-21868 is a high-severity denial of service vulnerability in Linux kernel, published on 27 Mar 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-21868 in the wild and no public exploit code.
Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.
Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.
Reference: https://insights.sbomify.com/CVE-2025-21868/ (Markdown: https://insights.sbomify.com/CVE-2025-21868/index.md)
```
## Sources
- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21868
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21868
- OSV: https://osv.dev/vulnerability/CVE-2025-21868
---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21868/
Summaries are generated and may contain mistakes; the official description above is the record.