libslirp CVE-2026-115449

Exploitation requires (1) a guest using libslirp-based user-mode ('slirp') networking, which is typically not the default in production virtualization (bridged/tap networking is more common), and (2) the specific host-side condition described: the normal ICMP socket being unavailable, forcing the fallback path in which the reply length is not updated to match the received data. The attacker must be a guest-level user capable of sending ICMP echo requests (PR:L). Because the triggering host condition is not attacker-controlled (AC:H), the leak cannot be forced reliably on demand. The impact is limited to disclosure of the host's real IP address (C:L); there is no code execution, write access, or denial of service. The trigger mechanism beyond the stated length-not-updated behavior and ICMP-socket-unavailable precondition is not further detailed in the available sources.

This is a low-severity information-disclosure issue (CVSS 3.5, CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:N/A:N) and the signals are internally consistent rather than conflicting. The Red Hat-assigned vector shows AC:H (the leak only occurs 'under specific conditions where the normal ICMP socket is unavailable', an attacker-uncontrolled precondition), PR:L (the attacker must already be a guest able to send ICMP), and a single low-confidentiality impact (C:L) limited to disclosure of the host's real IP address - there is no integrity or availability impact. The vuln.today Decision label is 'monitor', which aligns with the low score. No EPSS score, KEV listing, SSVC automatable/technical-impact values, or PoC reference is present in the supplied data, so there is no public exploit identified at time of analysis and no evidence of active exploitation; absence of these signals is not itself proof of safety but is consistent with a low-priority, non-emergency issue. The realistic harm is narrow: it erodes the NAT isolation that user-mode networking promises by revealing the host IP to the guest, which is reconnaissance value rather than code execution or data theft. This is a genuine but low-priority defect - appropriate to patch in routine maintenance, not an emergency. Note that AV:N reflects the guest sending ICMP over the virtual network; the exposure boundary is guest-to-host within a virtualization stack, not internet-facing.

An attacker with user-level access inside a virtual machine that uses libslirp (QEMU/KVM user-mode 'slirp' networking) sends ICMP echo requests. When the host's normal ICMP socket path is unavailable and the fallback code fails to resize the reply, the echo reply returned to the guest contains the host's real IP address, letting the guest fingerprint the host and defeat the expected NAT isolation. No public exploit code or PoC reference is present in the supplied data.