CVE-2026-115449

A flaw was found in libslirp. When handling ICMP echo requests, the reply length is not updated to match the actual data received from the host. Under specific conditions where the normal ICMP socket is unavailable, this length mismatch causes the host's real IP address to be leaked to the guest in the echo reply, breaking the NAT isolation that user-mode networking is expected to provide.

Red Hat has assessed this issue and confirmed a low-severity information disclosure. When the SOCK_DGRAM ICMP socket path is unavailable (ping_group_range restricted, which forces a raw socket fallback) and the guest pings a nonexistent host on the hypervisor's LAN, the host's real IP address can be leaked to the guest in the ICMP echo reply payload. This breaks NAT isolation but does not disclose arbitrary host heap memory as originally reported. The impact is limited to host IP address disclosure (4 bytes of network metadata). The normal SOCK_DGRAM ICMP path (used when ping_group_range is permissive) is not affected.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Ensure that the QEMU process user's GID is included in the system's ping_group_range (sysctl net.ipv4.ping_group_range), which allows the SOCK_DGRAM ICMP socket path and avoids the vulnerable raw socket fallback. Alternatively, use --net none or virtio-net with a TAP backend instead of user-mode (slirp) networking.