Vulnerability record · CVE-2026-53362 · published 4 July 2026
CVE-2026-53362: Linux kernel IPv6 UDP paged allocation out-of-bounds write
Linux · Linux Kernel
__ip6_append_data() in the Linux kernel mis-accounts fraggap on the paged-allocation path, leaving the linear skb area undersized while pagedlen is overstated, so a copy writes past skb->end into skb_shared_info. The flaw was introduced by commit 773ba4fe9104 and made triggerable by commit ce650a166335, which allowed MSG_SPLICE_PAGES to proceed instead of returning -EINVAL. It matters because an unprivileged local user can corrupt kernel heap memory through a UDPv6 socket.
Description
In the Linux kernel, the following vulnerability has been resolved: ipv6: account for fraggap on the paged allocation path In __ip6_append_data(), when the paged-allocation branch is taken (MSG_MORE / NETIF_F_SG / large fraglen), alloclen and pagedlen are computed as alloclen = fragheaderlen + transhdrlen; pagedlen = datalen - transhdrlen; datalen already includes fraggap (datalen = length + fraggap). When fraggap is non-zero, this is not the first skb and transhdrlen is zero. The fraggap bytes carried over from the previous skb are copied just past the fragment headers in the new skb's linear area. The linear area is therefore undersized by fraggap bytes while pagedlen is overstated by the same amount, and the copy writes past skb->end into the trailing skb_shared_info. An unprivileged user can trigger this via a UDPv6 socket using MSG_MORE together with MSG_SPLICE_PAGES. The bad accounting was introduced by commit 773ba4fe9104 ("ipv6: avoid partial copy for zc"). Before commit ce650a166335 ("udp6: Fix __ip6_append_data()'s handling of MSG_SPLICE_PAGES"), the negative copy value caused -EINVAL to be returned. That later commit allowed MSG_SPLICE_PAGES to proceed in this case, making the corruption triggerable. The non-paged branch sets alloclen to fraglen, which already accounts for fraggap because datalen does. Bring the paged branch in line by adding fraggap to alloclen and subtracting it from pagedlen. After this adjustment, copy no longer collapses to -fraggap on the paged path, so remove the stale comment describing that old arithmetic. Since a negative copy is no longer expected for a valid MSG_SPLICE_PAGES case, remove the MSG_SPLICE_PAGES exception from the negative copy check.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Automated analysis
high priorityThe flaw is a locally triggerable kernel heap out-of-bounds write with high C/I/A impact and is listed in CISA KEV, though it requires local low-privileged access and EPSS is low.
What it is
__ip6_append_data() in the Linux kernel mis-accounts fraggap on the paged-allocation path, leaving the linear skb area undersized while pagedlen is overstated, so a copy writes past skb->end into skb_shared_info. The flaw was introduced by commit 773ba4fe9104 and made triggerable by commit ce650a166335, which allowed MSG_SPLICE_PAGES to proceed instead of returning -EINVAL. It matters because an unprivileged local user can corrupt kernel heap memory through a UDPv6 socket.
Impact
An attacker gains an out-of-bounds write in kernel heap memory, which can lead to memory corruption and potential privilege escalation or denial of service. The CVSS vector rates confidentiality, integrity and availability impact as high.
Attack surface
Reached locally through a UDPv6 socket using MSG_MORE together with MSG_SPLICE_PAGES; the CVSS vector is AV:L/PR:L/UI:N, so low privileges are required and no user interaction is needed. No remote or network vector is described.
Exploitation
CVE-2026-53362 is listed in CISA KEV with a due date of 2026-08-30, indicating known exploitation, though no ransomware campaign use is documented. EPSS 30-day probability is 0.0051 (42.3rd percentile), and all references are patch or US Government resource links.
What to do
- Apply the upstream Linux kernel patches referenced in the git.kernel.org stable commits as soon as vendor builds are available.
- Follow CISA BOD 26-04 guidance and the KEV required action, including forensics triage where applicable.
- Restrict local unprivileged access to affected systems and reduce exposure of multi-tenant or container hosts running unpatched kernels.
- If patching is not immediately possible, evaluate discontinuing use of the affected product per CISA guidance for assets that cannot be mitigated.
Detection
- Monitor for kernel crashes, slab/heap corruption warnings or KASAN reports involving __ip6_append_data and skb_shared_info.
- Hunt for local processes making UDPv6 sends with MSG_MORE and MSG_SPLICE_PAGES, especially unusual or repeated patterns from unprivileged users.
- Track kernel version inventory against the patched stable commits to identify unpatched hosts.
- Review host telemetry for privilege escalation or anomalous kernel memory corruption activity on systems running affected kernels.
This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.
Exploitation in the wild
CISA added CVE-2026-53362 to the Known Exploited Vulnerabilities catalog on 27 August 2026 as "Linux Kernel Unspecified Vulnerability". Required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines. Federal deadline 30 August 2026.
Affected products
1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.
References
Track CVE-2026-53362 inside VULONE
Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.
Related vulnerabilities
Same products first, then exploited flaws of the same weakness class.
Source: NIST National Vulnerability Database (record CVE-2026-53362), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.
