cloudreve: Concurrent Execution using Shared Resource with Improper Synchronization
CVE-2026-77633 is a high-severity concurrent execution using shared resource with improper synchronization vulnerability in cloudreve, with a CVSS 3.1 base score of 7.1 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected cloudreve versions: < 4.18.0. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.37% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of cloudreve you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
Affected products and versions
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- LowLimited modification of data is possible.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H. Scored by CNA (github.com).
Official description
Cloudreve is a self-hosted file management and sharing system. Prior to 4.18.0, PrepareUpload in pkg/filemanager/fs/dbfs/upload.go checks a stale in-memory user storage value through validateUserCapacity and later applies an unconditional storage charge outside the same quota-enforcing transaction. An authenticated user with Files.Write permission can issue concurrent upload-session requests that read the same capacity snapshot, all pass the MaxStorage check, and reserve their declared sizes through CommitWithStorageDiff. The resulting reservations can exceed the account quota and can be materialized as chunked uploads that exhaust host storage and deny uploads to other users. The default local-storage policy and default User group are affected. This issue is fixed in version 4.18.0.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Concurrent Execution using Shared Resource with Improper Synchronization
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
How developers prevent this class of flaw
- In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.
- Use thread-safe capabilities such as the data access abstraction in Spring.
- Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring. Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other vulnerabilities in cloudreve
- 7.1 High severity
- 7.1 High severity
- 7.6 High severity
- 9.8 Critical severity
Recent Concurrent Execution using Shared Resource with Improper Synchronization vulnerabilities
- 8.1 High severity
- 7.0 High severity
- 7.0 High severity
- 7.0 High severity
- 7.0 High severity
- 8.8 High severity
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