EUVD-2026-76607
GHSA-rh54-vrwc-232g
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Network-reachable via NFS port 2049, no authentication beyond export membership, single-packet trigger, pure availability impact only.
Primary rating from Vendor (Linux).
CVSS VectorVendor: Linux
Lifecycle Timeline
6DescriptionCVE.org
In the Linux kernel, the following vulnerability has been resolved:
nfsd: cap decoded POSIX ACL count to bound sort cost
nfsd4_decode_posixacl() reads a u32 entry count off the wire and passes it straight to posix_acl_alloc() and sort_pacl_range(). The latter is an O(n^2) bubble sort, so a client-chosen count drives unbounded CPU in the server's compound processing path.
nfsd4_decode_posixacl() xdr_stream_decode_u32(&count) /* uncapped u32 */ posix_acl_alloc(count, GFP_KERNEL) sort_pacl_range(*acl, 0, count - 1) /* O(n^2) bubble sort */
The encoder side in the same file already rejects ACLs whose a_count exceeds NFS_ACL_MAX_ENTRIES, but the decoder introduced in commit 5fc51dfc2eb1 ("NFSD: Add support for XDR decoding POSIX draft ACLs") omitted the symmetric check.
Fix by rejecting a wire count greater than NFS_ACL_MAX_ENTRIES with nfserr_inval, before any allocation, so the sort is bounded by NFS_ACL_MAX_ENTRIES^2 comparisons.
While we're in here, also fix the nfserr_resource return if posix_acl_alloc() fails. That's not a legal error code for v4.1+. Change it to return nfserr_jukebox as that's more appropriate for memory allocation failures.
AnalysisAI
Unbounded O(n²) CPU consumption in the Linux kernel NFS server (nfsd) POSIX ACL decoder allows any NFS client reachable on port 2049 to cause server-side denial of service by supplying an oversized ACL entry count in a SETACL compound. The root cause is an asymmetry introduced in commit 5fc51dfc2eb1: the encoder already caps count at NFS_ACL_MAX_ENTRIES, but the decoder added in that commit omits the symmetric bound check, passing the raw wire u32 directly into an O(n²) bubble sort. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The Linux kernel NFS server (nfsd) must be running with NFSv4 support and POSIX ACL decoding enabled (compiled-in NFSACL support, active via export configuration). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 7.5 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) accurately captures the network-accessible, no-auth, pure-availability nature of this flaw. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Apply the vendor-released patches targeting Linux 7.2.4 or 7.3-rc1, available at https://git.kernel.org/stable/c/ea14d71d6ecb925673761bcf79f781f7dc9042cc and https://git.kernel.org/stable/c/4bc1108e876153a2dd6d874052b99182c3603135. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all Linux systems running NFS server (nfsd) and catalog current kernel versions against Linux 7.2.4 and 7.3-rc1 to establish remediation scope. …
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