Linux Kernel up to 6.18.54/7.2.8/7.3-rc4 UDP __udp_disconnect race condition

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
9.5	$0-$5k	0.00-

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.18.54/7.2.8/7.3-rc4 and classified as very critical. This impacts the function __udp_disconnect of the component UDP. Such manipulation leads to race condition. This vulnerability is referenced as CVE-2026-98595. It is possible to launch the attack remotely. No exploit is available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.18.54/7.2.8/7.3-rc4. It has been rated as very critical. Affected by this issue is the function __udp_disconnect of the component UDP. The manipulation with an unknown input leads to a race condition vulnerability. Using CWE to declare the problem leads to CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. Impacted is confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: udp: remove a disconnected socket from the 4-tuple hash table A UDP socket bound to a specific address and port keeps its entry in the 4-tuple hash table after it is disconnected: sk binds to 127.0.0.1:21001 sk connects to 127.0.0.2:20001 // filed in the 4-tuple table sk disconnects, connect(AF_UNSPEC) // still filed, peer now 0.0.0.0:0 __udp_disconnect() takes a socket out of that table only as a side effect of ->rehash() or ->unhash(), and it skips ->rehash() when SOCK_BINDADDR_LOCK is set and ->unhash() when SOCK_BINDPORT_LOCK is set. commit 6996a2d2d0a6 ("udp: Unhash auto-bound connected sk from 4-tuple hash table when disconnected.") fixed the same end state for a wildcard-bound socket, by a path this one does not take. The entry is counted whether or not anything hits it. hash4_cnt on the hash2 slot stays raised for as long as the socket lives, so udp_has_hash4() keeps sending every packet for that address and port through the 4-tuple lookup first. On IPv6 it can also be hit. __udp_disconnect() does not clear sk_v6_daddr, so udp_v6_rehash() files the entry under the peer the socket was connected to with a zero dport, and inet6_match() compares that same field: a datagram from the former peer with a zero source port matches, and source port zero is accepted on receive. On IPv4 the peer is cleared, so a match would need a zero source address as well, which the routing layer rejects as martian. The stale sk_v6_daddr is a separate defect, not addressed here; removing the entry closes this path either way. The entry can also be relocated. __udp_disconnect() clears sk_bound_dev_if, so a subsequent SO_BINDTODEVICE calls ->rehash(), and because the receive address is still specific udp_lib_rehash() moves the entry instead of removing it, into the bucket that (rcv_saddr, num, 0, 0) hashes to -- a pure function of the address and port, so every socket reaching this state on one address and port collects in one bucket. The bucket cannot be chosen from outside, as udp_ehashfn() is seeded with a per-boot secret. This last one became reachable only with commit 644f9108f3a5 ("udp: Make rehash4 independent in udp_lib_rehash()"), which moved the hash4 handling out of a branch a disconnected socket does not take; the stale entry itself dates from the commit in Fixes. Take the socket out of the table before __udp_disconnect() runs, while it still matches how it was filed. This also reaches the wildcard case ahead of udp_lib_rehash()'s udp_unhash4() branch, leaving that branch unreachable from udp_disconnect(); removing it belongs in net-next. udp_disconnect() and udp_abort() are the only UDP entries into __udp_disconnect(), which is shared with raw, ping and l2tp sockets that are not struct udp_sock: ping_prot.obj_size is sizeof(struct inet_sock), so udp_hashed4() on one would read past the allocation.

The advisory is available at git.kernel.org. This vulnerability is handled as CVE-2026-98595 since 09/25/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 10/18/2026).

Upgrading to version 6.18.55, 7.2.9 or 7.3-rc5 eliminates this vulnerability. Applying the patch c21daf37d5ce9a4e234b7c42238ac1e6041e28e4/d1b5fd969cc53f29d02b82b05a45135de4a6087a/9e95b1a94c9c49b4ba722251bbca2759b9c51737 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.18.0
• 6.18.1
• 6.18.2
• 6.18.3
• 6.18.4
• 6.18.5
• 6.18.6
• 6.18.7
• 6.18.8
• 6.18.9
• 6.18.10
• 6.18.11
• 6.18.12
• 6.18.13
• 6.18.14
• 6.18.15
• 6.18.16
• 6.18.17
• 6.18.18
• 6.18.19
• 6.18.20
• 6.18.21
• 6.18.22
• 6.18.23
• 6.18.24
• 6.18.25
• 6.18.26
• 6.18.27
• 6.18.28
• 6.18.29
• 6.18.30
• 6.18.31
• 6.18.32
• 6.18.33
• 6.18.34
• 6.18.35
• 6.18.36
• 6.18.37
• 6.18.38
• 6.18.39
• 6.18.40
• 6.18.41
• 6.18.42
• 6.18.43
• 6.18.44
• 6.18.45
• 6.18.46
• 6.18.47
• 6.18.48
• 6.18.49
• 6.18.50
• 6.18.51
• 6.18.52
• 6.18.53
• 6.18.54
• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5
• 7.2.6
• 7.2.7
• 7.2.8
• 7.3-rc1
• 7.3-rc2
• 7.3-rc3
• 7.3-rc4

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 10.0
VulDB Meta Temp Score: 9.5

VulDB Base Score: 10.0
VulDB Temp Score: 9.5
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AV	AC	Au	C	I	A
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳

Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock

VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Race condition
CWE: CWE-362
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.18.55/7.2.9/7.3-rc5
Patch: c21daf37d5ce9a4e234b7c42238ac1e6041e28e4/d1b5fd969cc53f29d02b82b05a45135de4a6087a/9e95b1a94c9c49b4ba722251bbca2759b9c51737

Timelineinfo

09/25/2026 CVE reserved
10/18/2026 +23 days Advisory disclosed
10/18/2026 +0 days VulDB entry created
10/18/2026 +0 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-98595 (🔒)
GCVE (CVE): GCVE-0-2026-98595
GCVE (VulDB): GCVE-100-422090

Entryinfo

Created: 10/18/2026 20:17
Changes: 10/18/2026 20:17 (59)
Complete: 🔍
Cache ID: 216::103

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Discussion

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