GHSA-vp4f-mc7f-v3pc · Severity: medium — In the Linux kernel, the following vulnerability has been resolved: dm thin: make get_first_thin...
In the Linux kernel, the following vulnerability has been resolved: dm thin: make get_first_thin use rcu-safe list first function The documentation in rculist.h explains the absence of list_empty_rcu() and cautions programmers against relying on a list_empty() -> list_first() sequence in RCU safe code. This is because each of these functions performs its own READ_ONCE() of the list head. This can lead to a situation where the list_empty() sees a valid list entry, but the subsequent list_first() sees a different view of list head state after a modification. In the case of dm-thin, this author had a production box crash from a GP fault in the process_deferred_bios path. This function saw a valid list head in get_first_thin() but when it subsequently dereferenced that and turned it into a thin_c, it got the inside of the struct pool, since the list was now empty and referring to itself. The kernel on which this occurred printed both a warning about a refcount_t being saturated, and a UBSAN error for an out-of-bounds cpuid access in the queued spinlock, prior to the fault itself. When the resulting kdump was examined, it was possible to see another thread patiently waiting in thin_dtr's synchronize_rcu. The thin_dtr call managed to pull the thin_c out of the active thins list (and have it be the last entry in the active_thins list) at just the wrong moment which lead to this crash. Fortunately, the fix here is straight forward. Switch get_first_thin() function to use list_first_or_null_rcu() which performs just a single READ_ONCE() and returns NULL if the list is already empty. This was run against the devicemapper test suite's thin-provisioning suites for delete and suspend and no regressions were observed.
Conclusion & alert: CVE-2025-21664 is rated Low Risk (24.7/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.03%). Mandatory action: Monitor for updates and reassess as exploit intelligence or EPSS changes.
Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.
EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).
| # | Date | Old EPSS score | New EPSS score | Delta (New - Old) |
|---|---|---|---|---|
| 1 | 2026-03-01 | 0.06% | 0.03% | -0.03% |
| 2 | 2025-11-04 | 0.04% | 0.06% | +0.01% |
| 3 | 2025-09-27 | — | 0.04% | — |
Full EPSS history (5 records total)
CVSS metrics for this CVE.
| Base score | Version | Severity | Vector | Exploitability | Impact | Score source |
|---|---|---|---|---|---|---|
| 5.5 | 3.1 | MEDIUM |
|
1.8 | 3.6 | [email protected] |
GHSA-vp4f-mc7f-v3pc · Severity: medium — In the Linux kernel, the following vulnerability has been resolved: dm thin: make get_first_thin...
| vendor | priority | summary | link |
|---|---|---|---|
debian
|
not yet assigned | CVE-2025-21664 not yet assigned priority: Debian including 2 source packages (linux, linux-6.1), 6 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 6. | https://security-tracker.debian.org/tracker/CVE-2025-21664 |
redhat
|
medium | — | https://access.redhat.com/security/cve/CVE-2025-21664 |
suse
|
medium | CVE-2025-21664 severity moderate: SUSE including 431 source package names (2.1.3-4.43:kernel-default-base-6.4.0-24.1.21.4, 2.1.3-6.5:kernel-default-6.4.0-25.1, …), 698 product×package rows across 128 product lines (Container suse/sl-micro/6.0/base-os-container, Container suse/sl-micro/6.0/kvm-os-container, … (128 product lines)): Fixed 442, Known Affected 231, Known Not Affected 25. | https://www.suse.com/security/cve/CVE-2025-21664/ |
ubuntu
|
medium | CVE-2025-21664 medium priority: Ubuntu including 158 source packages (linux, linux-allwinner-5.19, …), 1551 status rows across 10 suites (bionic, focal, jammy, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 1145, released 190, ignored 150, not-affected 46, needed 20. | https://ubuntu.com/security/CVE-2025-21664 |
| Vendor | Product | Version | Raw CPE |
|---|---|---|---|
| linux | linux_kernel | >= 3.15.1, < 5.4.290 | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
| linux | linux_kernel | >= 5.5, < 5.10.234 | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
| linux | linux_kernel | >= 5.11, < 5.15.177 | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
| linux | linux_kernel | >= 5.16, < 6.1.125 | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
| linux | linux_kernel | >= 6.2, < 6.6.72 | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
| linux | linux_kernel | >= 6.7, < 6.12.10 | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
| linux | linux_kernel | 3.15 | cpe:2.3:o:linux:linux_kernel:3.15:-:*:*:*:*:*:* |
| linux | linux_kernel | 3.15 | cpe:2.3:o:linux:linux_kernel:3.15:rc4:*:*:*:*:*:* |
| linux | linux_kernel | 3.15 | cpe:2.3:o:linux:linux_kernel:3.15:rc5:*:*:*:*:*:* |
| linux | linux_kernel | 3.15 | cpe:2.3:o:linux:linux_kernel:3.15:rc6:*:*:*:*:*:* |
| linux | linux_kernel | 3.15 | cpe:2.3:o:linux:linux_kernel:3.15:rc7:*:*:*:*:*:* |
| linux | linux_kernel | 3.15 | cpe:2.3:o:linux:linux_kernel:3.15:rc8:*:*:*:*:*:* |
| linux | linux_kernel | 6.13 | cpe:2.3:o:linux:linux_kernel:6.13:rc1:*:*:*:*:*:* |
| linux | linux_kernel | 6.13 | cpe:2.3:o:linux:linux_kernel:6.13:rc2:*:*:*:*:*:* |
| linux | linux_kernel | 6.13 | cpe:2.3:o:linux:linux_kernel:6.13:rc3:*:*:*:*:*:* |
| linux | linux_kernel | 6.13 | cpe:2.3:o:linux:linux_kernel:6.13:rc4:*:*:*:*:*:* |
| linux | linux_kernel | 6.13 | cpe:2.3:o:linux:linux_kernel:6.13:rc5:*:*:*:*:*:* |
| linux | linux_kernel | 6.13 | cpe:2.3:o:linux:linux_kernel:6.13:rc6:*:*:*:*:*:* |