CVE-2025-39950

net/tcp: Fix a NULL pointer dereference when using TCP-AO with TCP_REPAIR

5.5 MediumFix available

In the Linux kernel, the following vulnerability has been resolved:

net/tcp: Fix a NULL pointer dereference when using TCP-AO with TCP_REPAIR

A NULL pointer dereference can occur in tcp_ao_finish_connect() during a connect() system call on a socket with a TCP-AO key added and TCP_REPAIR enabled.

The function is called with skb being NULL and attempts to dereference it on tcp_hdr(skb)->seq without a prior skb validation.

Fix this by checking if skb is NULL before dereferencing it.

The commentary is taken from bpf_skops_established(), which is also called in the same flow. Unlike the function being patched, bpf_skops_established() validates the skb before dereferencing it.

int main(void){ struct sockaddr_in sockaddr; struct tcp_ao_add tcp_ao; int sk; int one = 1;

memset(&sockaddr,'\0',sizeof(sockaddr));
memset(&tcp_ao,'\0',sizeof(tcp_ao));

sk = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

sockaddr.sin_family = AF_INET;

memcpy(tcp_ao.alg_name,"cmac(aes128)",12);
memcpy(tcp_ao.key,"ABCDEFGHABCDEFGH",16);
tcp_ao.keylen = 16;

memcpy(&tcp_ao.addr,&sockaddr,sizeof(sockaddr));

setsockopt(sk, IPPROTO_TCP, TCP_AO_ADD_KEY, &tcp_ao,
sizeof(tcp_ao));
setsockopt(sk, IPPROTO_TCP, TCP_REPAIR, &one, sizeof(one));

sockaddr.sin_family = AF_INET;
sockaddr.sin_port = htobe16(123);

inet_aton("127.0.0.1", &sockaddr.sin_addr);

connect(sk,(struct sockaddr *)&sockaddr,sizeof(sockaddr));

return 0; }

$ gcc tcp-ao-nullptr.c -o tcp-ao-nullptr -Wall $ unshare -Urn

BUG: kernel NULL pointer dereference, address: 00000000000000b6 PGD 1f648d067 P4D 1f648d067 PUD 1982e8067 PMD 0 Oops: Oops: 0000 [#1] SMP NOPTI Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020 RIP: 0010:tcp_ao_finish_connect (net/ipv4/tcp_ao.c:1182)

Attack profile

How easy it is to exploit

Attack vector: Local
Complexity: Low
Privileges needed: Low
User interaction: None

What an attacker can affect

Confidentiality: None
Integrity: None
Availability: High

Exploit likelihood

0.15%Up 0.1 points since Oct 4, 2025

What each source reports

NVD Score used 5.5

In the Linux kernel, the following vulnerability has been resolved:

net/tcp: Fix a NULL pointer dereference when using TCP-AO with TCP_REPAIR

A NULL pointer dereference can occur in tcp_ao_finish_connect() during a connect() system call on a socket with a TCP-AO key added and TCP_REPAIR enabled.

The function is called with skb being NULL and attempts to dereference it on tcp_hdr(skb)->seq without a prior skb validation.

Fix this by checking if skb is NULL before dereferencing it.

The commentary is taken from bpf_skops_established(), which is also called in the same flow. Unlike the function being patched, bpf_skops_established() validates the skb before dereferencing it.

int main(void){ struct sockaddr_in sockaddr; struct tcp_ao_add tcp_ao; int sk; int one = 1;

memset(&sockaddr,'\0',sizeof(sockaddr));
memset(&tcp_ao,'\0',sizeof(tcp_ao));

sk = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

sockaddr.sin_family = AF_INET;

memcpy(tcp_ao.alg_name,"cmac(aes128)",12);
memcpy(tcp_ao.key,"ABCDEFGHABCDEFGH",16);
tcp_ao.keylen = 16;

memcpy(&tcp_ao.addr,&sockaddr,sizeof(sockaddr));

setsockopt(sk, IPPROTO_TCP, TCP_AO_ADD_KEY, &tcp_ao,
sizeof(tcp_ao));
setsockopt(sk, IPPROTO_TCP, TCP_REPAIR, &one, sizeof(one));

sockaddr.sin_family = AF_INET;
sockaddr.sin_port = htobe16(123);

inet_aton("127.0.0.1", &sockaddr.sin_addr);

connect(sk,(struct sockaddr *)&sockaddr,sizeof(sockaddr));

return 0; }

$ gcc tcp-ao-nullptr.c -o tcp-ao-nullptr -Wall $ unshare -Urn

Record: CVE-2025-39950
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-476
Updated: 2026-11-02

CVE List No score

net/tcp: Fix a NULL pointer dereference when using TCP-AO with TCP_REPAIR

In the Linux kernel, the following vulnerability has been resolved:

net/tcp: Fix a NULL pointer dereference when using TCP-AO with TCP_REPAIR

A NULL pointer dereference can occur in tcp_ao_finish_connect() during a connect() system call on a socket with a TCP-AO key added and TCP_REPAIR enabled.

The function is called with skb being NULL and attempts to dereference it on tcp_hdr(skb)->seq without a prior skb validation.

Fix this by checking if skb is NULL before dereferencing it.

The commentary is taken from bpf_skops_established(), which is also called in the same flow. Unlike the function being patched, bpf_skops_established() validates the skb before dereferencing it.

int main(void){ struct sockaddr_in sockaddr; struct tcp_ao_add tcp_ao; int sk; int one = 1;

memset(&sockaddr,'\0',sizeof(sockaddr));
memset(&tcp_ao,'\0',sizeof(tcp_ao));

sk = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

sockaddr.sin_family = AF_INET;

memcpy(tcp_ao.alg_name,"cmac(aes128)",12);
memcpy(tcp_ao.key,"ABCDEFGHABCDEFGH",16);
tcp_ao.keylen = 16;

memcpy(&tcp_ao.addr,&sockaddr,sizeof(sockaddr));

setsockopt(sk, IPPROTO_TCP, TCP_AO_ADD_KEY, &tcp_ao,
sizeof(tcp_ao));
setsockopt(sk, IPPROTO_TCP, TCP_REPAIR, &one, sizeof(one));

sockaddr.sin_family = AF_INET;
sockaddr.sin_port = htobe16(123);

inet_aton("127.0.0.1", &sockaddr.sin_addr);

connect(sk,(struct sockaddr *)&sockaddr,sizeof(sockaddr));

return 0; }

$ gcc tcp-ao-nullptr.c -o tcp-ao-nullptr -Wall $ unshare -Urn

Record: CVE-2025-39950
Updated: 2026-11-02

EUVDEUVD-2025-32392 No score

In the Linux kernel, the following vulnerability has been resolved:

net/tcp: Fix a NULL pointer dereference when using TCP-AO with TCP_REPAIR

A NULL pointer dereference can occur in tcp_ao_finish_connect() during a connect() system call on a socket with a TCP-AO key added and TCP_REPAIR enabled.

The function is called with skb being NULL and attempts to dereference it on tcp_hdr(skb)->seq without a prior skb validation.

Fix this by checking if skb is NULL before dereferencing it.

The commentary is taken from bpf_skops_established(), which is also called in the same flow. Unlike the function being patched, bpf_skops_established() validates the skb before dereferencing it.

int main(void){ struct sockaddr_in sockaddr; struct tcp_ao_add tcp_ao; int sk; int one = 1;

memset(&sockaddr,'\0',sizeof(sockaddr));
memset(&tcp_ao,'\0',sizeof(tcp_ao));

sk = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

sockaddr.sin_family = AF_INET;

memcpy(tcp_ao.alg_name,"cmac(aes128)",12);
memcpy(tcp_ao.key,"ABCDEFGHABCDEFGH",16);
tcp_ao.keylen = 16;

memcpy(&tcp_ao.addr,&sockaddr,sizeof(sockaddr));

setsockopt(sk, IPPROTO_TCP, TCP_AO_ADD_KEY, &tcp_ao,
sizeof(tcp_ao));
setsockopt(sk, IPPROTO_TCP, TCP_REPAIR, &one, sizeof(one));

sockaddr.sin_family = AF_INET;
sockaddr.sin_port = htobe16(123);

inet_aton("127.0.0.1", &sockaddr.sin_addr);

connect(sk,(struct sockaddr *)&sockaddr,sizeof(sockaddr));

return 0; }

$ gcc tcp-ao-nullptr.c -o tcp-ao-nullptr -Wall $ unshare -Urn

Record: EUVD-2025-32392
Updated: 2026-11-02

GitHub AdvisoriesGHSA-f4h6-hf7g-852r 5.5

In the Linux kernel, the following vulnerability has been resolved: net/tcp: Fix a NULL pointer...

In the Linux kernel, the following vulnerability has been resolved:

net/tcp: Fix a NULL pointer dereference when using TCP-AO with TCP_REPAIR

A NULL pointer dereference can occur in tcp_ao_finish_connect() during a connect() system call on a socket with a TCP-AO key added and TCP_REPAIR enabled.

The function is called with skb being NULL and attempts to dereference it on tcp_hdr(skb)->seq without a prior skb validation.

Fix this by checking if skb is NULL before dereferencing it.

The commentary is taken from bpf_skops_established(), which is also called in the same flow. Unlike the function being patched, bpf_skops_established() validates the skb before dereferencing it.

int main(void){ struct sockaddr_in sockaddr; struct tcp_ao_add tcp_ao; int sk; int one = 1;

memset(&sockaddr,'\0',sizeof(sockaddr));
memset(&tcp_ao,'\0',sizeof(tcp_ao));

sk = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

sockaddr.sin_family = AF_INET;

memcpy(tcp_ao.alg_name,"cmac(aes128)",12);
memcpy(tcp_ao.key,"ABCDEFGHABCDEFGH",16);
tcp_ao.keylen = 16;

memcpy(&tcp_ao.addr,&sockaddr,sizeof(sockaddr));

setsockopt(sk, IPPROTO_TCP, TCP_AO_ADD_KEY, &tcp_ao,
sizeof(tcp_ao));
setsockopt(sk, IPPROTO_TCP, TCP_REPAIR, &one, sizeof(one));

sockaddr.sin_family = AF_INET;
sockaddr.sin_port = htobe16(123);

inet_aton("127.0.0.1", &sockaddr.sin_addr);

connect(sk,(struct sockaddr *)&sockaddr,sizeof(sockaddr));

return 0; }

$ gcc tcp-ao-nullptr.c -o tcp-ao-nullptr -Wall $ unshare -Urn

Record: GHSA-f4h6-hf7g-852r
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-476
Updated: 2026-11-02

OSVBELL-CVE-2025-39950 5.5

Record: BELL-CVE-2025-39950
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVDEBIAN-CVE-2025-39950 5.5

In the Linux kernel, the following vulnerability has been resolved: net/tcp: Fix a NULL pointer dereference when using TCP-AO with TCP_REPAIR A NULL pointer dereference can occur in tcp_ao_finish_connect() during a connect() system call on a socket with a TCP-AO key added and TCP_REPAIR enabled. The function is called with skb being NULL and attempts to dereference it on tcp_hdr(skb)->seq without a prior skb validation. Fix this by checking if skb is NULL before dereferencing it. The commentary is taken from bpf_skops_established(), which is also called in the same flow. Unlike the function being patched, bpf_skops_established() validates the skb before dereferencing it. int main(void){ struct sockaddr_in sockaddr; struct tcp_ao_add tcp_ao; int sk; int one = 1; memset(&sockaddr,'\0',sizeof(sockaddr)); memset(&tcp_ao,'\0',sizeof(tcp_ao)); sk = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); sockaddr.sin_family = AF_INET; memcpy(tcp_ao.alg_name,"cmac(aes128)",12); memcpy(tcp_ao.key,"ABCDEFGHABCDEFGH",16); tcp_ao.keylen = 16; memcpy(&tcp_ao.addr,&sockaddr,sizeof(sockaddr)); setsockopt(sk, IPPROTO_TCP, TCP_AO_ADD_KEY, &tcp_ao, sizeof(tcp_ao)); setsockopt(sk, IPPROTO_TCP, TCP_REPAIR, &one, sizeof(one)); sockaddr.sin_family = AF_INET; sockaddr.sin_port = htobe16(123); inet_aton("127.0.0.1", &sockaddr.sin_addr); connect(sk,(struct sockaddr *)&sockaddr,sizeof(sockaddr)); return 0; } $ gcc tcp-ao-nullptr.c -o tcp-ao-nullptr -Wall $ unshare -Urn BUG: kernel NULL pointer dereference, address: 00000000000000b6 PGD 1f648d067 P4D 1f648d067 PUD 1982e8067 PMD 0 Oops: Oops: 0000 [#1] SMP NOPTI Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020 RIP: 0010:tcp_ao_finish_connect (net/ipv4/tcp_ao.c:1182)

Record: DEBIAN-CVE-2025-39950
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

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OSVROOT-OS-UBUNTU-2404-CVE-2025-39950 5.5

CVE-2025-39950 in linux - Patched by Root

Root has patched CVE-2025-39950 in the linux package for Root:Ubuntu:24.04. Multiple fixed versions available.

Record: ROOT-OS-UBUNTU-2404-CVE-2025-39950
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-06

OSVUBUNTU-CVE-2025-39950 6.8

Record: UBUNTU-CVE-2025-39950
CVSS 4.0: 6.8 MediumCVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-11

OSV No score