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CVE-2026-31503— udp: Fix wildcard bind conflict check when using hash2

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.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于UDP通配符绑定冲突检查在使用hash2时存在逻辑错误，可能导致地址冲突检测失败。

AI Predicted 5.3 Difficulty: Moderate EPSS 0.12% · P2

Possible ATT&CK Techniques 2 AI

T1071 · Application Layer Protocol T1042

Affected Version Matrix 14

VendorProduct Version RangeStatus
Linux Linux 30fff9231fad757c061285e347b33c5149c2c2e4< d6ace0dbcbb7fd285738bb87b42b71b01858c952 affected
30fff9231fad757c061285e347b33c5149c2c2e4< 2297e38114316b26ae02f2d205c49b5511c5ed55 affected
30fff9231fad757c061285e347b33c5149c2c2e4< f1bed05a832ae79be5f7a105da56810eaa59a5f1 affected
30fff9231fad757c061285e347b33c5149c2c2e4< 18d84c45def3671d5c89fbdd5d4ab8a3217fe4b4 affected
30fff9231fad757c061285e347b33c5149c2c2e4< 0a360f7f73a06ac88f18917055fbcc79694252d7 affected
30fff9231fad757c061285e347b33c5149c2c2e4< e537dd15d0d4ad989d56a1021290f0c674dd8b28 affected
2.6.33 affected
< 2.6.33 unaffected
… +6 more rows
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I. Basic Information for CVE-2026-31503

Vulnerability Information
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Vulnerability Title
udp: Fix wildcard bind conflict check when using hash2
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: udp: Fix wildcard bind conflict check when using hash2 When binding a udp_sock to a local address and port, UDP uses two hashes (udptable->hash and udptable->hash2) for collision detection. The current code switches to "hash2" when hslot->count > 10. "hash2" is keyed by local address and local port. "hash" is keyed by local port only. The issue can be shown in the following bind sequence (pseudo code): bind(fd1, "[fd00::1]:8888") bind(fd2, "[fd00::2]:8888") bind(fd3, "[fd00::3]:8888") bind(fd4, "[fd00::4]:8888") bind(fd5, "[fd00::5]:8888") bind(fd6, "[fd00::6]:8888") bind(fd7, "[fd00::7]:8888") bind(fd8, "[fd00::8]:8888") bind(fd9, "[fd00::9]:8888") bind(fd10, "[fd00::10]:8888") /* Correctly return -EADDRINUSE because "hash" is used * instead of "hash2". udp_lib_lport_inuse() detects the * conflict. */ bind(fail_fd, "[::]:8888") /* After one more socket is bound to "[fd00::11]:8888", * hslot->count exceeds 10 and "hash2" is used instead. */ bind(fd11, "[fd00::11]:8888") bind(fail_fd, "[::]:8888") /* succeeds unexpectedly */ The same issue applies to the IPv4 wildcard address "0.0.0.0" and the IPv4-mapped wildcard address "::ffff:0.0.0.0". For example, if there are existing sockets bound to "192.168.1.[1-11]:8888", then binding "0.0.0.0:8888" or "[::ffff:0.0.0.0]:8888" can also miss the conflict when hslot->count > 10. TCP inet_csk_get_port() already has the correct check in inet_use_bhash2_on_bind(). Rename it to inet_use_hash2_on_bind() and move it to inet_hashtables.h so udp.c can reuse it in this fix.
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
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于UDP通配符绑定冲突检查在使用hash2时存在逻辑错误，可能导致地址冲突检测失败。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 30fff9231fad757c061285e347b33c5149c2c2e4 ~ d6ace0dbcbb7fd285738bb87b42b71b01858c952 -
Linux Linux 2.6.33 -

II. Public POCs for CVE-2026-31503

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III. Intelligence Information for CVE-2026-31503

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Same Patch Batch · Linux · 2026-04-22 · 100 CVEs total

CVE-2026-31463 9.8 CRITICAL iomap: fix invalid folio access when i_blkbits differs from I/O granularity
CVE-2026-31444 9.8 CRITICAL ksmbd: fix use-after-free and NULL deref in smb_grant_oplock()
CVE-2026-31501 9.8 CRITICAL net: ti: icssg-prueth: fix use-after-free of CPPI descriptor in RX path
CVE-2026-31436 9.8 CRITICAL dmaengine: idxd: fix possible wrong descriptor completion in llist_abort_desc()
CVE-2026-31478 9.8 CRITICAL ksmbd: replace hardcoded hdr2_len with offsetof() in smb2_calc_max_out_buf_len()
CVE-2026-31448 9.4 CRITICAL ext4: avoid infinite loops caused by residual data
CVE-2026-31432 8.8 HIGH ksmbd: fix OOB write in QUERY_INFO for compound requests
CVE-2026-31433 8.8 HIGH ksmbd: fix potencial OOB in get_file_all_info() for compound requests
CVE-2026-31450 8.8 HIGH ext4: publish jinode after initialization
CVE-2026-31435 8.8 HIGH netfs: Fix read abandonment during retry
CVE-2026-31476 8.2 HIGH ksmbd: do not expire session on binding failure
CVE-2026-31464 8.1 HIGH scsi: ibmvfc: Fix OOB access in ibmvfc_discover_targets_done()
CVE-2026-31513 8.1 HIGH Bluetooth: L2CAP: Fix stack-out-of-bounds read in l2cap_ecred_conn_req
CVE-2026-31504 7.8 HIGH net: fix fanout UAF in packet_release() via NETDEV_UP race
CVE-2026-31449 7.8 HIGH ext4: validate p_idx bounds in ext4_ext_correct_indexes
CVE-2026-31502 7.8 HIGH team: fix header_ops type confusion with non-Ethernet ports
CVE-2026-31431 7.8 HIGH crypto: algif_aead - Revert to operating out-of-place
CVE-2026-31488 7.8 HIGH drm/amd/display: Do not skip unrelated mode changes in DSC validation
CVE-2026-31490 7.8 HIGH drm/xe/pf: Fix use-after-free in migration restore
CVE-2026-31454 7.8 HIGH xfs: save ailp before dropping the AIL lock in push callbacks

Showing top 20 of 100 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-31503

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