High

Linux kernel IPv4 UDP corking heap out-of-bounds write

IdentifiersCVE-2026-53366CWE-787

CVE-2026-53366 is a heap out-of-bounds write in the Linux kernel IPv4 UDP corking path. The flaw is in __ip_append_data() when the paged-allocation branch is used during packet construction. In the vulnerable logic, datalen already includes fraggap, but the paged path computes alloclen as fragheaderlen plus transhdrlen and pagedlen as datalen minus transhdrlen, omitting fraggap from the linear allocation while still effectively accounting for it in the copied data. Subsequent copying of the fraggap bytes into the new skb linear area at offset transhdrlen causes the linear area to be undersized by fraggap bytes and pagedlen to be overstated by the same amount. Under the reachable UDP corking and MSG_SPLICE_PAGES conditions, this results in a controlled heap out-of-bounds write into skb_shared_info. The disclosed overwrite size is 15 bytes, and the issue affects the IPv4 UDP path in Linux kernel versions from v6.1 onward.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can corrupt adjacent kernel heap metadata or structures associated with the socket buffer, specifically skb_shared_info. The disclosed effect is a controlled 15-byte overwrite that can be used to manipulate fields such as nr_frags, causing stale fragment state to be treated as valid. This memory corruption is assessed as exploitable for local privilege escalation. Kernel crashes and denial of service are also plausible outcomes if exploitation is unsuccessful or unstable.

Mitigation

If you can’t patch tonight, do this now.

If immediate patching is not possible, reduce exposure by restricting local untrusted code execution, especially in environments where unprivileged users can create the required socket and splice conditions. Limit or disable unprivileged user namespaces where operationally feasible, because the IPv4 variant is noted as requiring USERNS. Harden multi-tenant systems by preventing untrusted local users from accessing kernel attack surface associated with UDP corking and splice-based workflows until patched. These measures only reduce exploitability and do not eliminate the underlying flaw.

Remediation

Patch, then assume compromise.

Update to a Linux kernel version containing the upstream fix for CVE-2026-53366. The fix corrects fraggap accounting in the IPv4 paged allocation path by adding fraggap to alloclen and subtracting it from pagedlen, aligning the paged branch with the non-paged logic. The fix also removes the stale arithmetic assumption that allowed the negative-copy condition on this path. Systems running kernels from v6.1 onward should be upgraded to a release that includes commit eca856950f7c or an equivalent backport from the vendor.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

LinuxLinux Kerneloperating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

8 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

8 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

The version that knows your environment.

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity8

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-53366

NVD

nvd.nist.gov/vuln/detail/CVE-2026-53366

MITRE CWE · CWE-787

cwe.mitre.org

git.kernel.org

git.kernel.org/stable/c/77798d7be6ef71e72fb6fc8a2901bf74ebc9706f

git.kernel.org

git.kernel.org/stable/c/a9c24eda24bd15f432e37824e6fc440977cb241c

git.kernel.org

git.kernel.org/stable/c/c04d9ece23deb9e26c19f9ca215e98b3295aa1bb

git.kernel.org

git.kernel.org/stable/c/ce494707a9c07f27c219ca67f3e138061f53d9b3

git.kernel.org

git.kernel.org/stable/c/eca856950f7cb1a221e02b99d758409f2c5cec42

Linux kernel IPv4 UDP corking heap out-of-bounds write

IdentifiersCVE-2026-53366CWE-787