VulnerabilityPublished 14 Oct 2026Updated 19 Oct 2026

CVE-2026-98393: Linux kernel · net: ipv4: Fix UDP length overflow with PMTU discover and big MTU

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in b83641e0ab8b20eefcc4cdc5a059f897375291a2 : update Linux kernel when convenient.

Data as of 26 Oct 2026, 17:16 UTC

Severity

Medium

Rated Medium by Threat Radar's AI analysis · CVSS not yet scored by NVD

EPSS: 0.2% chance of exploitation in 30 days – higher than 10% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in b83641e0ab8b20eefcc4cdc5a059f897375291a2, 83fedc4741210f75be8ca5b487985a242bf6f18d, 81f540827d243b8dad76c1f44e70ea31719f393c

Exploitation evidence

Disclosed: evidence found.
CVE published 14 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Linux kernel to b83641e0ab8b20eefcc4cdc5a059f897375291a2, 83fedc4741210f75be8ca5b487985a242bf6f18d or 81f540827d243b8dad76c1f44e70ea31719f393c.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ daba287b299ec7a2c61ae3a714920e90e8396ad5, < b83641e0ab8b20eefcc4cdc5a059f897375291a2	Fixed in b83641e0ab8b20eefcc4cdc5a059f897375291a2
LinuxLinux	Affected ≥ daba287b299ec7a2c61ae3a714920e90e8396ad5, < 83fedc4741210f75be8ca5b487985a242bf6f18d	Fixed in 83fedc4741210f75be8ca5b487985a242bf6f18d
LinuxLinux	Affected ≥ daba287b299ec7a2c61ae3a714920e90e8396ad5, < 81f540827d243b8dad76c1f44e70ea31719f393c	Fixed in 81f540827d243b8dad76c1f44e70ea31719f393c
LinuxLinux	Affected =3.13	Fixed in–

AI-suggested

The vulnerability has been fixed in the Linux kernel in commits b83641e0ab8b20eefcc4cdc5a059f897375291a2, 83fedc4741210f75be8ca5b487985a242bf6f18d, and 81f540827d243b8dad76c1f44e70ea31719f393c. Users and administrators should update to a Linux kernel version that includes these commits to remediate the issue. No additional mitigation steps are indicated.

Description

A vulnerability in the Linux kernel IPv4 implementation could cause a UDP length overflow when Path MTU Discovery (PMTU) is set to probe mode and the network device MTU is unusually large. This overflow triggers a warning in the kernel and is caused by improper bounding of fragment size during packet construction. The issue has been fixed in specific kernel commits.

Impact

The vulnerability causes a UDP length overflow that triggers a kernel warning, which may lead to instability or unexpected behavior in the network stack when sending large UDP packets with PMTU discovery set to probe mode on devices with large MTUs. There is no indication of remote code execution or privilege escalation. No known exploits in the wild have been reported.

Summary

CVE-2026-98393 addresses a UDP length overflow vulnerability in the Linux kernel's IPv4 networking stack. When the device MTU is set larger than IP_MAX_MTU plus 20 bytes and IP_MTU_DISCOVER is set to IP_PMTUDISC_PROBE, the cork->base.fragsize is incorrectly set to the device MTU, allowing the UDP length field to overflow the 16-bit limit (65536). This triggers a WARN in udp_set_len_short. The vulnerability arises because the UDP length is not properly bounded, leading to an overflow when sending large packets over a network device with a large MTU. The fix bounds cork->base.fragsize to IP_MAX_MTU, preventing the overflow. The vulnerability does not affect IP_PMTUDISC_DO mode due to clamping at IP_MAX_MTU. The fix is included in specific Linux kernel commits identified by their hashes.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 11:33 UTC

Technical details

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