CVE-2025-39879 Vulnerability Analysis & Exploit Details

CVE-2025-39879
Vulnerability Scoring

Analysis In Progress
Analysis In Progress

Attack Complexity Details

  • Attack Complexity:
    Attack Complexity Analysis In Progress
  • Attack Vector:
    Attack Vector Under Analysis
  • Privileges Required: None
    No authentication is required for exploitation.
  • Scope:
    Impact is confined to the initially vulnerable component.
  • User Interaction: None
    No user interaction is necessary for exploitation.

CVE-2025-39879 Details

Status: Received on 23 Sep 2025, 06:15 UTC

Published on: 23 Sep 2025, 06:15 UTC

CVSS Release:

CVE-2025-39879 Vulnerability Summary

CVE-2025-39879: In the Linux kernel, the following vulnerability has been resolved: ceph: always call ceph_shift_unused_folios_left() The function ceph_process_folio_batch() sets folio_batch entries to NULL, which is an illegal state. Before folio_batch_release() crashes due to this API violation, the function ceph_shift_unused_folios_left() is supposed to remove those NULLs from the array. However, since commit ce80b76dd327 ("ceph: introduce ceph_process_folio_batch() method"), this shifting doesn't happen anymore because the "for" loop got moved to ceph_process_folio_batch(), and now the `i` variable that remains in ceph_writepages_start() doesn't get incremented anymore, making the shifting effectively unreachable much of the time. Later, commit 1551ec61dc55 ("ceph: introduce ceph_submit_write() method") added more preconditions for doing the shift, replacing the `i` check (with something that is still just as broken): - if ceph_process_folio_batch() fails, shifting never happens - if ceph_move_dirty_page_in_page_array() was never called (because ceph_process_folio_batch() has returned early for some of various reasons), shifting never happens - if `processed_in_fbatch` is zero (because ceph_process_folio_batch() has returned early for some of the reasons mentioned above or because ceph_move_dirty_page_in_page_array() has failed), shifting never happens Since those two commits, any problem in ceph_process_folio_batch() could crash the kernel, e.g. this way: BUG: kernel NULL pointer dereference, address: 0000000000000034 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: Oops: 0002 [#1] SMP NOPTI CPU: 172 UID: 0 PID: 2342707 Comm: kworker/u778:8 Not tainted 6.15.10-cm4all1-es #714 NONE Hardware name: Dell Inc. PowerEdge R7615/0G9DHV, BIOS 1.6.10 12/08/2023 Workqueue: writeback wb_workfn (flush-ceph-1) RIP: 0010:folios_put_refs+0x85/0x140 Code: 83 c5 01 39 e8 7e 76 48 63 c5 49 8b 5c c4 08 b8 01 00 00 00 4d 85 ed 74 05 41 8b 44 ad 00 48 8b 15 b0 > RSP: 0018:ffffb880af8db778 EFLAGS: 00010207 RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000003 RDX: ffffe377cc3b0000 RSI: 0000000000000000 RDI: ffffb880af8db8c0 RBP: 0000000000000000 R08: 000000000000007d R09: 000000000102b86f R10: 0000000000000001 R11: 00000000000000ac R12: ffffb880af8db8c0 R13: 0000000000000000 R14: 0000000000000000 R15: ffff9bd262c97000 FS: 0000000000000000(0000) GS:ffff9c8efc303000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000034 CR3: 0000000160958004 CR4: 0000000000770ef0 PKRU: 55555554 Call Trace: <TASK> ceph_writepages_start+0xeb9/0x1410 The crash can be reproduced easily by changing the ceph_check_page_before_write() return value to `-E2BIG`. (Interestingly, the crash happens only if `huge_zero_folio` has already been allocated; without `huge_zero_folio`, is_huge_zero_folio(NULL) returns true and folios_put_refs() skips NULL entries instead of dereferencing them. That makes reproducing the bug somewhat unreliable. See https://lore.kernel.org/20250826231626.218675-1-max.kellermann@ionos.com for a discussion of this detail.) My suggestion is to move the ceph_shift_unused_folios_left() to right after ceph_process_folio_batch() to ensure it always gets called to fix up the illegal folio_batch state.

Assessing the Risk of CVE-2025-39879

Access Complexity Graph

The exploitability of CVE-2025-39879 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).

Exploitability Analysis for CVE-2025-39879

No exploitability data is available for CVE-2025-39879.

Understanding AC and PR

A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.

Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.

Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.

CVSS Score Breakdown Chart

Above is the CVSS Sub-score Breakdown for CVE-2025-39879, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.

CIA Impact Analysis

Below is the Impact Analysis for CVE-2025-39879, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.

  • Confidentiality: None
    CVE-2025-39879 does not compromise confidentiality.
  • Integrity: None
    CVE-2025-39879 does not impact data integrity.
  • Availability: None
    CVE-2025-39879 does not affect system availability.

CVE-2025-39879 References

External References

CWE Common Weakness Enumeration

Unknown

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