{"id":"CVE-2026-31538","state":"PUBLISHED","title":"smb: server: make use of smbdirect_socket.recv_io.credits.available","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: server: make use of smbdirect_socket.recv_io.credits.available\n\nThe logic off managing recv credits by counting posted recv_io and\ngranted credits is racy.\n\nThat's because the peer might already consumed a credit,\nbut between receiving the incoming recv at the hardware\nand processing the completion in the 'recv_done' functions\nwe likely have a window where we grant credits, which\ndon't really exist.\n\nSo we better have a decicated counter for the\navailable credits, which will be incremented\nwhen we posted new recv buffers and drained when\nwe grant the credits to the peer.\n\nThis fixes regression Namjae reported with\nthe 6.18 release.","publishedAt":"2026-04-24T14:30:25.598Z","updatedAt":"2026-08-05T12:23:22.947Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"89b021a72663c4d96d8a8b85272bb42d991a1c6f","status":"affected","lessThan":"66c082e3d4651e8629a393a9e182b01eb50fb0a3","versionType":"git"},{"version":"89b021a72663c4d96d8a8b85272bb42d991a1c6f","status":"affected","lessThan":"809cbd31aa4f87a1b889532244c9cf30eb022385","versionType":"git"},{"version":"89b021a72663c4d96d8a8b85272bb42d991a1c6f","status":"affected","lessThan":"26ad87a2cfb8c1384620d1693a166ed87303046e","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/transport_rdma.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.18","versionType":"semver"},{"version":"6.18.11","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.1","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/transport_rdma.c"]}],"references":["https://git.kernel.org/stable/c/66c082e3d4651e8629a393a9e182b01eb50fb0a3","https://git.kernel.org/stable/c/809cbd31aa4f87a1b889532244c9cf30eb022385","https://git.kernel.org/stable/c/26ad87a2cfb8c1384620d1693a166ed87303046e"],"weaknesses":[],"ingestedAt":"2026-10-29T20:11:40.391Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/31xxx/CVE-2026-31538.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-31538","state":"PUBLISHED","datePublished":"2026-04-24T14:30:25.598Z","dateUpdated":"2026-08-05T12:23:22.947Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-03-09T15:48:24.113Z"},"containers":{"cna":{"title":"smb: server: make use of smbdirect_socket.recv_io.credits.available","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: server: make use of smbdirect_socket.recv_io.credits.available\n\nThe logic off managing recv credits by counting posted recv_io and\ngranted credits is racy.\n\nThat's because the peer might already consumed a credit,\nbut between receiving the incoming recv at the hardware\nand processing the completion in the 'recv_done' functions\nwe likely have a window where we grant credits, which\ndon't really exist.\n\nSo we better have a decicated counter for the\navailable credits, which will be incremented\nwhen we posted new recv buffers and drained when\nwe grant the credits to the peer.\n\nThis fixes regression Namjae reported with\nthe 6.18 release."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"89b021a72663c4d96d8a8b85272bb42d991a1c6f","status":"affected","lessThan":"66c082e3d4651e8629a393a9e182b01eb50fb0a3","versionType":"git"},{"version":"89b021a72663c4d96d8a8b85272bb42d991a1c6f","status":"affected","lessThan":"809cbd31aa4f87a1b889532244c9cf30eb022385","versionType":"git"},{"version":"89b021a72663c4d96d8a8b85272bb42d991a1c6f","status":"affected","lessThan":"26ad87a2cfb8c1384620d1693a166ed87303046e","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/transport_rdma.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.18","versionType":"semver"},{"version":"6.18.11","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.1","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/transport_rdma.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/66c082e3d4651e8629a393a9e182b01eb50fb0a3"},{"url":"https://git.kernel.org/stable/c/809cbd31aa4f87a1b889532244c9cf30eb022385"},{"url":"https://git.kernel.org/stable/c/26ad87a2cfb8c1384620d1693a166ed87303046e"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - SMB Direct is a network-facing ksmbd RDMA transport listening on SMB/RDMA ports, and the vulnerable credit path is reached by packets from a remote SMB Direct peer. The attacker only needs network access to the exposed SMB Direct service.\nAC:L - The race is between receive completion processing and server credit grants, but the attacker controls the RDMA connection traffic and can repeatedly pipeline/flood requests to hit the window. No unusual victim-side condition is required beyond SMB Direct being enabled.\nPR:N - The affected path is in SMB Direct transport negotiation and data transfer handling before SMB session authentication is required. A remote unauthenticated peer can reach the credit accounting logic.\nUI:N - No victim user action is needed after the ksmbd SMB Direct service is running. The attacker triggers the issue by connecting and sending SMB Direct traffic.\nS:U - The impact remains within the kernel ksmbd/SMB Direct service security authority. There is no VM escape, sandbox escape, or cross-scope boundary change.\nC:N - The bug is receive-credit accounting, not an out-of-bounds access, use-after-free, or disclosure path. It does not provide a defensible kernel memory read primitive.\nI:N - Over-granting receive credits does not grant authorization or create a write primitive into kernel memory. The RDMA receive path consumes posted receive buffers and fails/disconnects when credits are invalid rather than allowing attacker-controlled memory modification.\nA:H - The peer can be granted credits for receive buffers that no longer exist, leading to RDMA receive-not-ready/QP errors or disconnects. Because this can be triggered remotely and repeatedly without authentication, it can deny SMB Direct service availability."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:23:22.947Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18","versionEndExcluding":"6.18.11"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18","versionEndExcluding":"6.19.1"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18","versionEndExcluding":"7.0"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}