CVE-2023-53083 in Linux
Summary
by MITRE • 05/02/2025
In the Linux kernel, the following vulnerability has been resolved:
nfsd: don't replace page in rq_pages if it's a continuation of last page
The splice read calls nfsd_splice_actor to put the pages containing file data into the svc_rqst->rq_pages array. It's possible however to get a splice result that only has a partial page at the end, if (e.g.) the filesystem hands back a short read that doesn't cover the whole page.
nfsd_splice_actor will plop the partial page into its rq_pages array and return. Then later, when nfsd_splice_actor is called again, the remainder of the page may end up being filled out. At this point, nfsd_splice_actor will put the page into the array _again_ corrupting the reply. If this is done enough times, rq_next_page will overrun the array and corrupt the trailing fields -- the rq_respages and rq_next_page pointers themselves.
If we've already added the page to the array in the last pass, don't add it to the array a second time when dealing with a splice continuation. This was originally handled properly in nfsd_splice_actor, but commit 91e23b1c3982 ("NFSD: Clean up nfsd_splice_actor()") removed the check for it.
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Analysis
by VulDB Data Team • 11/13/2025
The vulnerability described in CVE-2023-53083 resides within the Linux kernel's Network File System Daemon (nfsd) implementation, specifically affecting how the nfsd_splice_actor function handles page management during splice read operations. This flaw represents a critical memory corruption issue that can lead to system instability and potential privilege escalation. The vulnerability manifests when the nfsd service processes file data through the svc_rqst->rq_pages array, which serves as a buffer for storing pages containing file data during network file operations. The core issue stems from improper handling of partial page scenarios that occur during filesystem read operations, particularly when the filesystem returns short reads that don't fill complete pages. This vulnerability directly impacts the integrity of the kernel's memory management system and can result in severe operational consequences for systems running NFS services.
The technical flaw occurs within the nfsd_splice_actor function where the system attempts to manage page data during splice operations by placing pages into the svc_rqst->rq_pages array. When filesystem operations return partial pages, the function incorrectly processes these continuation pages by adding the same page to the array multiple times instead of recognizing that the page was already added during a previous operation. This duplication occurs because the function fails to check whether the current page was already stored in the array during the previous pass through the splice operation. The original implementation correctly handled this scenario, but a code cleanup commit 91e23b1c3982 inadvertently removed this crucial validation check, leaving the system vulnerable to repeated page insertion. The vulnerability is classified under CWE-129 as an "Improper Validation of Array Index" and represents a classic case of buffer over-read conditions that can lead to memory corruption.
The operational impact of this vulnerability extends beyond simple data corruption, potentially enabling attackers to exploit the memory corruption for privilege escalation or denial of service attacks. When the nfsd_splice_actor function encounters partial pages during splice operations, it continues to insert the same page multiple times into the rq_pages array, eventually causing the rq_next_page pointer to exceed the allocated array boundaries. This overrunning behavior corrupts adjacent memory regions including the rq_respages and rq_next_page pointers themselves, which can lead to unpredictable system behavior, kernel panics, or even allow malicious actors to execute arbitrary code with kernel privileges. The vulnerability is particularly dangerous in environments where NFS services are heavily utilized, as it can be triggered through normal file access operations. According to ATT&CK framework category T1068, this vulnerability could be leveraged for privilege escalation, while T1499 covers potential denial of service scenarios that may result from the memory corruption.
Mitigation strategies for CVE-2023-53083 should prioritize applying the official kernel patch that restores the proper validation check in nfsd_splice_actor function to prevent duplicate page insertion. System administrators should immediately update their Linux kernel installations to versions containing the fix, as this vulnerability can be exploited remotely through NFS service access. Additionally, monitoring should be implemented to detect unusual NFS service behavior or memory allocation patterns that might indicate exploitation attempts. Network segmentation can help limit the attack surface by restricting access to NFS services, while disabling unnecessary NFS functionality on systems that do not require it provides an additional defensive layer. The fix specifically addresses the root cause by ensuring that pages already present in the svc_rqst->rq_pages array during the previous processing pass are not reinserted during subsequent continuation operations, thereby maintaining the integrity of the memory management system and preventing the array overrun condition that leads to memory corruption.