PwnEscape (CVE-2026-99999)

Incident Report for CloudLinux

Update

Livepatch is in the production feed for all EL 8, 9 and 10 kernels.
- el8: AlmaLinux 8 (K20261021_0008), RHEL 8 (K20261021_0003), Oracle Linux 8 (K20261021_0005), Rocky Linux 8 (K20261021_0009). Production 2026-10-21, ePortal 2026-10-23.
- el9: RHEL 9 and AlmaLinux 9 / CloudLinux 9 are in ePortal since 2026-10-19.
- el10: RHEL 10 in production since 2026-10-19. AlmaLinux 10 / CloudLinux 10 in ePortal since 2026-10-21.

Livepatch for other distros:
- Debian 13 (K20261022_0015): production 2026-10-22, ePortal 2026-10-26.
- Ubuntu 26.04 (K20261020_0011): production 2026-10-20, ePortal 2026-10-23.
- Ubuntu 24.04 (K20261024_0010): production since 2026-10-26.
- Proxmox VE 8 (K20261024_0013): production since 2026-10-26.
- In progress: Debian 12, Ubuntu 22.04, Ubuntu 20.04, CentOS 7.
- No release yet for CloudLinux 7 and CloudLinux 8.

CentOS 7 is affected. Red Hat fixed it in the RHEL 7 ELS kernel 3.10.0-1160.167.2.el7 (RHSA-2026:88206).

Vendor kernels are now available:
- Red Hat: RHEL 8 (RHSA-2026:89083, 4.18.0-553.178.1.el8_10), RHEL 9 (RHSA-2026:86033, 5.14.0-687.59.1.el9_8), RHEL 10 (RHSA-2026:85321, 6.12.0-211.67.1.el10_2), and several EUS kernels.
- Debian: bookworm 6.1.190-1, trixie 6.12.113-1.
- Ubuntu: fixed kernels for 22.04, 24.04 and 26.04 are pending release. 20.04 and 18.04 still need a fix.

No public exploit code
Posted Oct 27, 2026 - 08:38 UTC

Update

CVE-2026-99999 (CVSS 9.3 Critical) is a flaw in how the Linux kernel handles IPv4 checksum metadata from virtio-net. An untrusted virtual machine (VM) guest can overwrite two bytes of an already-validated IPv4 header on the host. The researcher reports a host memory leak, a host crash, and code execution as root on a test host.

No public proof-of-concept exists, and we have not reproduced the attack.

Affected: every supported CloudLinux kernel line is expected to carry the vulnerable code. Hosts that run untrusted VM guests are exposed on every version. Shared hosts without VMs are exposed only where unprivileged users can create user namespaces.
Mitigation: partial and untested. Turn off checksum offload for untrusted guests, and disable unprivileged user namespaces to close the local path.
Fix status: no fixed kernel has shipped yet.
Stream 1, CloudLinux kernel (CloudLinux 7h, 8): in preparation, waiting for the upstream fix.
Stream 2, AlmaLinux kernel (CloudLinux 9, 10): waiting for the AlmaLinux fix.
Stream 3, TuxCare ELS kernel (CloudLinux 8 LTS, 9 LTS): pending ELS release.
Stream 4, KernelCare livepatch: EL9 family released:
K20261016_0001: RHEL 9 - in testing
K20261016_0002: AlmaLinux 9 and CloudLinux 9 - currently in the main feed
K20261016_0004: Oracle Linux 9 - in testing
K20261016_0005 / K20261016_0006: Rocky Linux 9 - in testing

Patchsets for other systems still in progress.


Verify: uname -r against the target version, or kcarectl --patch-info | grep CVE-2026-99999

You can find more detailed information on our blog: CVE-2026-99999
Posted Oct 16, 2026 - 17:34 UTC

Update

KernelCare livepatch is currently available in the test feed for the EL9 family and will be released to the main feed later today.

K20261016_0001: RHEL 9
K20261016_0002: AlmaLinux 9 and CloudLinux 9
K20261016_0004: Oracle Linux 9
K20261016_0005 / K20261016_0006: Rocky Linux 9
Posted Oct 16, 2026 - 11:21 UTC

Identified

A vulnerability exists in the Linux kernel’s IPv4 networking code that could allow a malicious virtual machine guest to damage memory within the host kernel by sending specially crafted packets. Remote network access alone is insufficient to exploit this flaw; the attacker must already be able to execute code inside a VM or on the server. Systems running KVM with untrusted virtual machines face the greatest risk.

At this time, no publicly available exploit code has been identified. Technical details have been published in a write-up, and there are no known reports of exploitation in the wild.

Status:
- Upstream fix exists. Red Hat has not published its assessment or a fix yet.
- We decided not to wait for the vendor here. KernelCare patch is in progress (KCARE-32844), no ETA yet

Affected distros/kernels:
CentOS7 3.10 - Vulnerable
Debian12 6.1 - Vulnerable
Debian13 6.12 - Vulnerable
Ubuntu24.04 6.8 - Vulnerable
Ubuntu26.04 7.0 - Vulnerable
Almalinux8 4.18 - Local Privilege Escalation Possible
Almalinux9 5.14 - Local Privilege Escalation Possible
Almalinux10 6.12 - Local Privilege Escalation Possible
Posted Oct 15, 2026 - 23:02 UTC