CVE-2026-89098: Nfs-utils: nfs-utils: denial of service via assertion failure in fsidd

AIONLYREPORT package: nfs-utils-2.8.3-5.el102 ------ Summary: Local DoS in fsidd via Reachable assert() on Empty Command Arguments: a local unprivileged user can terminate fsidd by sending a malformed command containing only a valid command prefix and trailing space, causing a denial of service for reexport FSID lookups until the daemon is restarted. Requirements to exploit: Local access to a system where fsidd is running for reexport functionality, with the ability to connect to its abstract UNIX domain socket and send a crafted request. Component affected: nfs-utils; support/reexport/fsidd.c; clientcb() Version affected: nfs-utils-2.8.3-5.el102, when fsidd is present and in use for reexport workflows Patch available: no released package fix established; proposed patch included below Version fixed: unknown Upstream coordination: Not notified. CVSS: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - 5.5 (MEDIUM) AV:L - Exploitation requires local access to the host and access to the fsidd UNIX socket. AC:L - A single malformed request is sufficient to reach the failing assertion. PR:N - No protocol-level authentication is required before the request is parsed. UI:N - No user interaction is needed once local access is available. S:U - The impact is limited to the vulnerable service itself. C:N - No confidentiality impact was established. I:N - No integrity impact was established. A:H - Successful exploitation aborts fsidd, disrupting FSID lookup handling for reexport use until restart. Impact: Moderate. This issue enables a reliable local denial of service against fsidd, but the impact is limited to availability and depends on a deployment that actually uses fsidd for reexport handling. Under Red Hat's severity guidance, this is more appropriately Moderate than Important because it is not a remote flaw, does not expose confidentiality or integrity, and affects a configuration-dependent service path rather than a broadly reachable default remote attack surface. Embargo: no Reason: This is a local, configuration-dependent denial of service with straightforward mitigation and no demonstrated confidentiality, integrity, or privilege-escalation impact. Acknowledgement: Aisle Research Vulnerability Details: In clientcb(), fsidd parses several commands received over its local socket and relies on assert() to enforce that an argument is present after the command prefix. The following exact checks are reachable from untrusted input: c if (strncmp(buf, "getfsidnum ", strlen("getfsidnum ")) == 0) { char reqpath = buf + strlen("getfsidnum "); ... assert(reqpath < buf + n ); } ... } else if (strncmp(buf, "getorcreatefsidnum ", strlen("getorcreatefsidnum ")) == 0) { char reqpath = buf + strlen("getorcreatefsidnum "); ... assert(reqpath < buf + n ); } ... } else if (strncmp(buf, "getpath ", strlen("getpath ")) == 0) { char reqfsidnum = buf + strlen("getpath "); ... assert(reqfsidnum < buf + n ); } If a request is exactly the command prefix plus a trailing space, such as getfsidnum , then the parsed argument pointer is equal to buf + n and the assertion fails. In an assertion-enabled build, this causes fsidd to abort. The default socket name is defined as an abstract UNIX socket: c #define FSIDSOCKETNAME "@/run/fsid.sock" Based on the available code and report evidence, fsidd processes requests on this socket without checking peer credentials first, so local socket access is sufficient to reach the vulnerable path. The operational effect is a local denial of service against fsidd, which can interrupt reexport FSID lookup handling until the service is restarted. Steps to reproduce: 1. Use a system where fsidd is running for reexport handling. 2. Verify that the service is active. bash systemctl status fsidd 3. Send a malformed command containing a valid command name, trailing space, and no argument to the abstract UNIX seqpacket socket. bash python3 - <<'PY' import socket s = socket.socket(socket.AFUNIX, socket.SOCKSEQPACKET) s.connect("\0/run/fsid.sock") s.sendall(b"getfsidnum ") PY 4. Observe that fsidd terminates with an assertion failure or SIGABRT, for example in the service journal. bash journalctl -u fsidd -n 20 --no-pager 5. Confirm that reexport FSID lookup operations fail until fsidd is restarted. Mitigation: Where reexport support is not required, disable the affected fsidd usage path. Otherwise, restrict untrusted local access to the host and apply input validation so malformed requests are rejected instead of reaching assert(). A service restart policy may reduce outage duration, but it does not prevent the crash condition. Proposed Fix: Replace the reachable assertions with explicit malformed-input handling and return an error to the client. diff diff --git a/support/reexport/fsidd.c b/support/reexport/fsidd.c — a/support/reexport/fsidd.c +++ b/support/reexport/fsidd.c @@ -48,7 +48,12 @@ static void clientcb(evutilsockett cl, short ev, void d) char answer = NULL; bool found; - assert(reqpath < buf + n ); + if (reqpath >= buf + n) { + char answer[] = "- Command failed: Bad input"; + (void)send(cl, answer, strlen(answer), 0); + return; + } @@ -70,7 +75,12 @@ static void clientcb(evutilsockett cl, short ev, void d) char answer = NULL; bool found; - assert(reqpath < buf + n ); + if (reqpath >= buf + n) { + char answer[] = "- Command failed: Bad input"; + (void)send(cl, answer, strlen(answer), 0); + return; + } @@ -94,7 +104,12 @@ static void clientcb(evutilsockett cl, short ev, void d) uint32t fsidnum; bool found; - assert(reqfsidnum < buf + n ); + if (reqfsidnum >= buf + n) { + char answer[] = "- Command failed: Bad input"; + (void)send(cl, answer, strlen(answer), 0); + return; + } ------ This report was generated using AI technology. 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— Red Hat

Nfs-utils: nfs-utils: denial of service via assertion failure in fsidd

— Microsoft