CVE-2026-89544
moderateNULL deref, refcount leak in Linux kernel SUNRPC gss-proxy XDR decode error paths
The Linux kernel's SUNRPC gssx XDR decoder, used when the kernel delegates RPCSEC_GSS Kerberos context establishment to the userspace gss-proxy daemon, contains four coupled error-path defects. On a decoding failure, gssx_dec_option_array() can return with count=1 while data is NULL, which the caller gssp_accept_sec_context_upcall() then dereferences, producing a kernel NULL-dereference oops; the error paths also leak the refcounted group_info allocation (a path to remote memory exhaustion through repeated requests) and harbor a latent use-after-free in credential teardown. An unauthenticated remote attacker sending crafted RPC/RPCSEC_GSS data to an NFS or other RPC server whose Kerberos credentials are handled via gss-proxy (typical of FreeIPA/Active Directory-joined deployments) can trigger these paths and crash or degrade the server. Impact is availability only (CVSS 3.1 7.5, A:H); there is no public PoC and no known exploitation to date.
What to do: Apply a kernel update containing the upstream SUNRPC gssx error-path fix as soon as your distribution ships it and reboot to load the patched kernel. In the interim, restrict NFS/RPC ports (2049 and the rpcbind port 111) to trusted networks and verify whether gss-proxy is actually in use — systems handling RPCSEC_GSS via the traditional rpc.gssd upcalls are not on the vulnerable path. Watch server logs for kernel oopses in gssp_accept_sec_context_upcall() and for unexplained memory growth attributable to group_info leaks on gss-proxy servers.
| Linux kernel (SUNRPC/gss-proxy gssx XDR decoder) | Upstream kernel versions prior to the fix commit "SUNRPC: fix gssx_dec_option_array error path bugs"; no specific version ranges were provided in the advisory |
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
In the Linux kernel, the following vulnerability has been resolved: SUNRPC: fix gssx_dec_option_array error path bugs Four coupled defects in the gssx XDR option-array decoder make the error paths unsafe: a NULL deref in the caller, a refcount leak on the decoded group_info, and a latent use-after-free that the leak fix would otherwise expose. gssx_dec_option_array() sets oa->count = 1 before allocating oa->data. If that allocation fails, -ENOMEM is returned with oa->count == 1 and oa->data == NULL. All other error paths jump to free_oa: which frees oa->data and NULLs it but also leaves oa->count == 1. The caller trusts the count: gssp_accept_sec_context_upcall() gssx_dec_accept_sec_context() gssx_dec_option_array() /* fails, count=1 data=NULL */ data = res.options.data[0].value /* NULL deref */ Independently, free_creds: releases the partially decoded svc_cred with a bare kfree(creds). gssx_dec_linux_creds() installs a groups_alloc() result into creds->cr_group_info; that object is kvmalloc-backed and refcounted, and only put_group_info() reaches kvfree(). A plain kfree(creds) drops the wrapper and leaks the group_info allocation. The natural fix for the leak is to call free_svc_cred(creds) before kfree(creds), but free_svc_cred() invokes put_group_info() on creds->cr_group_info unconditionally when non-NULL. The existing out_free_groups: path in gssx_dec_linux_creds() already called groups_free() on that pointer without clearing it, so once free_svc_cred() is wired in, the subsequent put_group_info() would touch freed memory. Fix all four together: - Move the oa->count = 1 assignment below the oa->data allocation so it is never set when oa->data is NULL. - Reset oa->count to 0 at free_oa: so count and data stay coherent and the caller sees an empty option array. - Call free_svc_cred(creds) before kfree(creds) at free_creds: so the refcounted cr_group_info is released. free_svc_cred() either NULL-guards each field explicitly (cr_group_info has an if() check) or delegates to a helper that is NULL-safe itself (kfree for the string fields, gss_mech_put() which guards with if(gm) at gss_mech_switch.c:342), so it is safe to call on a partially decoded svc_cred where only cr_uid/cr_gid/cr_group_info have been written and everything else is zero from kzalloc. - In gssx_dec_linux_creds()'s out_free_groups: path, release cr_group_info with put_group_info() rather than groups_free() so the teardown matches free_svc_cred()'s refcount-aware path, and clear the pointer so a later free_svc_cred() on the same creds does not release it a second time.
- Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
In the news0 stories
No ingested article mentions this CVE yet.