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

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

In the Linux kernel, the following vulnerability has been resolved: net: ipv4: Fix UDP length overflow with PMTU discover and big MTU This commit bounds cork->base.fragsize to IP_MAX_MTU to avoid a possible overflow of UDP length that triggers a WARN in udp_se

Affected Version Matrix 8

VendorProduct Version RangeStatus
Linux Linux daba287b299ec7a2c61ae3a714920e90e8396ad5< 83fedc4741210f75be8ca5b487985a242bf6f18d affected
daba287b299ec7a2c61ae3a714920e90e8396ad5< 81f540827d243b8dad76c1f44e70ea31719f393c affected
daba287b299ec7a2c61ae3a714920e90e8396ad5< b83641e0ab8b20eefcc4cdc5a059f897375291a2 affected
3.13 affected
< 3.13 unaffected
6.18.53≤ 6.18.* unaffected
7.2.7≤ 7.2.* unaffected
7.3-rc3≤ * unaffected
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I. Basic Information for CVE-2026-98393

Vulnerability Information

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Vulnerability Title
net: ipv4: Fix UDP length overflow with PMTU discover and big MTU
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: net: ipv4: Fix UDP length overflow with PMTU discover and big MTU This commit bounds cork->base.fragsize to IP_MAX_MTU to avoid a possible overflow of UDP length that triggers a WARN in udp_set_len_short when setsockopt IP_MTU_DISCOVER is set to IP_PMTUDISC_PROBE, and a large packet is sent over a netdev with an unusually large MTU. Steps to reproduce: 1. Set device MTU bigger than IP_MAX_MTU + 20. cork->base.fragsize will be set to that MTU in ip_setup_cork. 2. Set IP_MTU_DISCOVER to IP_PMTUDISC_PROBE. It lets maxnonfragsize be set to device MTU (cork->fragsize) in __ip_append_data, rather than to IP_MAX_MTU. 3. Send 65528 bytes of payload (+8 bytes of UDP header, +20 bytes of IPv4 header). Device MTU allows it (it's only one byte bigger than IP_MAX_MTU + IPv4 header, and the device MTU is bigger than that). 4. The UDP length in the built packet is 65536, which overflows the 16-bit length field and triggers the WARN in udp_set_len_short. Note: IP_PMTUDISC_DO with IPv4 is safe, because ip_dst_mtu_maybe_forward always clamps at IP_MAX_MTU, unlike ip6_dst_mtu_maybe_forward. The Fixes tag points at the first commit where I could reproduce the overflow with IPv4 and IP_PMTUDISC_PROBE.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux daba287b299ec7a2c61ae3a714920e90e8396ad5 ~ 83fedc4741210f75be8ca5b487985a242bf6f18d -
Linux Linux 3.13 -

II. Public POCs for CVE-2026-98393

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III. Intelligence Information for CVE-2026-98393

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Other References for CVE-2026-98393 (3)

Same Patch Batch · Linux · 2026-10-14 · 46 CVEs total

CVE-2026-98399 s390/ipl: Fix NULL deref in dump_reipl without re-IPL parm block
CVE-2026-98395 powerpc/entry: Fix irq_soft_mask corruption on replayed interrupt exit
CVE-2026-98394 af_unix: Return immediately when manage_oob() returns NULL for 0-length buffer.
CVE-2026-98391 drm/xe: Guard page-fault worker with runtime PM check
CVE-2026-98389 drm/amdgpu: skip gfx switch_power_profile during GPU reset
CVE-2026-98388 exec: do_close_on_exec() before taking exec_update_lock
CVE-2026-98387 s390/crypto: Fix skcipher_walk return code handling in aes_s390
CVE-2026-98386 scsi: qla2xxx: Use memset_io() to clear QLAFX00 request ring slot
CVE-2026-98390 x86/amd_node: Avoid divide by zero on virtualized systems
CVE-2026-98398 locking/lockdep: Invalidate stale class_cache entries for zapped classes
CVE-2026-98397 platform/x86: x86-android-tablets: hold device reference for secondary fwnode teardown
CVE-2026-98400 s390/ipl: Fix NULL deref in kdump without re-IPL parm block
CVE-2026-98402 net: icmp: avoid invalid transport header access in icmp_send tracepoint
CVE-2026-98401 net: iptunnel: fix stale transport header during tunnel decapsulation
CVE-2026-98403 s390/boot: Avoid IPL parameter append past command line
CVE-2026-98404 drm/virtio: Fix a NULL vs ERR_PTR() bug in virtio_gpu_user_framebuffer_create()
CVE-2026-98405 smb: client: fix missing iov bounds check in parse_posix_sids()
CVE-2026-98406 wifi: mac80211: avoid WARN in set_bitrate_mask when sdata not in driver
CVE-2026-98408 watchdog: rzv2h: Avoid division by zero
CVE-2026-98407 wifi: rsi: fix heap OOB write on key removal

Showing top 20 of 46 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

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