CVE-2025-39738 — btrfs: do not allow relocation of partially dropped subvolumes
In the Linux kernel, the following vulnerability has been resolved: btrfs: do not allow relocation of partially dropped subvolumes [BUG] There is an internal report that balance triggered transaction abort, with the following call trace: item 85 key (594509824 169 0) itemoff 12599 itemsize 33 extent refs 1 gen 197740 flags 2 ref#0: tree block backref root 7 item 86 key (594558976 169 0) itemoff 12566 itemsize 33 extent refs 1 gen 197522 flags 2 ref#0: tree block backref root 7 ... BTRFS error (device loop0): extent item not found for insert, bytenr 594526208 num_bytes 16384 parent 449921024 root_objectid 934 owner 1 offset 0 BTRFS error (device loop0): failed to run delayed ref for logical 594526208 num_bytes 16384 type 182 action 1 ref_mod 1: -117 ------------[ cut here ]------------ BTRFS: Transaction aborted (error -117) WARNING: CPU: 1 PID: 6963 at ../fs/btrfs/extent-tree.c:2168 btrfs_run_delayed_refs+0xfa/0x110 [btrfs] And btrfs check doesn't report anything wrong related to the extent tree. [CAUSE] The cause is a little complex, firstly the extent tree indeed doesn't have the backref for 594526208. The extent tree only have the following two backrefs around that bytenr on-disk: item 65 key (594509824 METADATA_ITEM 0) itemoff 13880 itemsize 33 refs 1 gen 197740 flags TREE_BLOCK tree block skinny level 0 (176 0x7) tree block backref root CSUM_TREE item 66 key (594558976 METADATA_ITEM 0) itemoff 13847 itemsize 33 refs 1 gen 197522 flags TREE_BLOCK tree block skinny level 0 (176 0x7) tree block backref root CSUM_TREE But the such missing backref item is not an corruption on disk, as the offending delayed ref belongs to subvolume 934, and that subvolume is being dropped: item 0 key (934 ROOT_ITEM 198229) itemoff 15844 itemsize 439 generation 198229 root_dirid 256 bytenr 10741039104 byte_limit 0 bytes_used 345571328 last_snapshot 198229 flags 0x1000000000001(RDONLY) refs 0 drop_progress key (206324 EXTENT_DATA 2711650304) drop_level 2 level 2 generation_v2 198229 And that offending tree block 594526208 is inside the dropped range of that subvolume. That explains why there is no backref item for that bytenr and why btrfs check is not reporting anything wrong. But this also shows another problem, as btrfs will do all the orphan subvolume cleanup at a read-write mount. So half-dropped subvolume should not exist after an RW mount, and balance itself is also exclusive to subvolume cleanup, meaning we shouldn't hit a subvolume half-dropped during relocation. The root cause is, there is no orphan item for this subvolume. In fact there are 5 subvolumes from around 2021 that have the same problem. It looks like the original report has some older kernels running, and caused those zombie subvolumes. Thankfully upstream commit 8d488a8c7ba2 ("btrfs: fix subvolume/snapshot deletion not triggered on mount") has long fixed the bug. [ENHANCEMENT] For repairing such old fs, btrfs-progs will be enhanced. Considering how delayed the problem will show up (at run delayed ref time) and at that time we have to abort transaction already, it is too late. Instead here we reject any half-dropped subvolume for reloc tree at the earliest time, preventing confusion and extra time wasted on debugging similar bugs.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.2% (30-day exploitation probability)+1
- Technical severity (high)+6
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, Linux Linux, Linux Linux Kernel).
- Apply the fixed version or the patch documented under Remediation.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Debian | Debian Linux | version 11.0 | Vulnerable | NIST National Vulnerability Database |
| Linux | Linux | version 5.11≥ 638331fa56caeaa8b4d31cc1dfbe0ce989bcff67 and < 4289b494ac553e74e86fed1c66b2bf9530bc1082≥ 638331fa56caeaa8b4d31cc1dfbe0ce989bcff67 and < 4e403bd8e127d40dc7c05f06ee969c1ba1537ec5≥ 638331fa56caeaa8b4d31cc1dfbe0ce989bcff67 and < 125e94a4b76b7b75d194f85bedd628097d2121f0≥ 638331fa56caeaa8b4d31cc1dfbe0ce989bcff67 and < 39a93e1c9dbf7e11632efeb20fcf0fc1dcf64d51≥ 638331fa56caeaa8b4d31cc1dfbe0ce989bcff67 and < f83d4c81bda3b7d1813268ab77408f7a0ce691ff≥ 638331fa56caeaa8b4d31cc1dfbe0ce989bcff67 and < fcb1f77b8ed8795608ca7a1f6505e2b07236c1f3≥ 638331fa56caeaa8b4d31cc1dfbe0ce989bcff67 and < fa086b1398cf7e5f7dee7241bd5f2855cb5df8dc | Vulnerable | CVE Program (cve.org) e CISA ADP |
| Linux | Linux Kernel |
version 5.11-rc6version 6.17-rc1version 5.11-rc7version 5.11-rc5version 5.11-rc4version 5.11-rc3version 5.11≥ 6.16 and < 6.16.2 and 5 more≥ 6.13 and < 6.15.11≥ 6.7 and < 6.12.43≥ 6.2 and < 6.6.103≥ 5.16 and < 6.1.149≥ 5.11.1 and < 5.15.190 |
Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 7.8 | CVSS 3.1 | High | 1.8 | 5.9 | nvd@nist.gov via NIST National Vulnerability Database |
| 7.8 | CVSS 3.1 | High | — | — | GitHub, Inc. via GitHub Security Advisories |
| 7.3 | CVSS 3.1 | High | 1.8 | 5.5 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database |
| 7.3 | CVSS 3.1 | High | — | — | Linux via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (score shown at the top: nvd@nist.gov) Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · linux/linux
- SSVC assessment updated
- Record published
- Fix documented
- Affected products added · linux/linux kernel, debian/debian linux
- CVSS changed · 7.8
- Source status changed · → Modified
- Record created in this database
- 2025
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 2× References added · Oct 15, 2026 – Oct 15, 2026
- 1× Official description updated · Oct 15, 2026 – Oct 15, 2026
References
11 on the record
- git.kernel.org/stable/c/fa086b1398cf7e5f7dee7241bd5f2855cb5df8dc
- git.kernel.org/stable/c/fcb1f77b8ed8795608ca7a1f6505e2b07236c1f3
- git.kernel.org/stable/c/f83d4c81bda3b7d1813268ab77408f7a0ce691ff
- git.kernel.org/stable/c/4289b494ac553e74e86fed1c66b2bf9530bc1082
- git.kernel.org/stable/c/125e94a4b76b7b75d194f85bedd628097d2121f0
- git.kernel.org/stable/c/4e403bd8e127d40dc7c05f06ee969c1ba1537ec5
- git.kernel.org/stable/c/39a93e1c9dbf7e11632efeb20fcf0fc1dcf64d51
- cert-portal.siemens.com/productcert/html/ssa-032379.html
- lists.debian.org/debian-lts-announce/2025/10/msg00008.html
- github.com/advisories/GHSA-8x83-vv5w-vmh3
- nvd.nist.gov/vuln/detail/CVE-2025-39738
Elsewhere on this site
Related CVEs (same products)
- Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 13h
- Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 13h
- Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
- Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
- Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
- Unknown CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No CWE classification.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2025-39738 is "btrfs: do not allow relocation of partially dropped subvolumes", rated High. It affects Debian Linux (Debian); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.8 describes technical severity. EPSS 0.18% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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