Discuz! X5.0: Reusing a Nonce, Key Pair in Encryption
CVE-2026-49952 is a critical-severity reusing a nonce, key pair in encryption vulnerability in Discuz! X5.0 from Discuz!, with a CVSS 3.1 base score of 9.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected Discuz! X5.0 versions: 20260320 through 20260501. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 4.72% chance of exploitation within 30 days, which is in the top 8.03% of all scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Check which version of Discuz! X5.0 you run against the affected versions below, and install the vendor's latest release.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Discuz! | Discuz! X5.0 | 20260320 through 20260501 | Not stated |
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
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. Scored by CNA (vulncheck.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 9.3 | Critical | CNA (vulncheck.com) |
| CVSS 3.1 | 9.1 | Critical | CNA (vulncheck.com) |
Official description
Discuz! X5.0 releases 20260320 through 20260501 contains an authentication bypass vulnerability that allows unauthenticated remote attackers to gain unauthorized access to database backup and restore functionality by exploiting a shared cryptographic key between UCenter integration and the database backup API exposed by dbbak.php. Attackers can inject a crafted payload through the username parameter during login to abuse the encryption oracle in logging_ctl::logging_more(), obtain a legitimately signed token, and use it to bypass authorization for database export and import operations, with the additional ability to trigger a race condition to impersonate arbitrary users.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Reusing a Nonce, Key Pair in Encryption
Nonces should be used for the present occasion and only once.
How developers prevent this class of flaw
- Use techniques such as requiring incrementing, time based and/or challenge response to assure uniqueness of nonces.
More Reusing a Nonce, Key Pair in Encryption vulnerabilities (CWE-323)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other references
Other vulnerabilities in Discuz! X5.0
- 7.2 High severity
Recent Reusing a Nonce, Key Pair in Encryption vulnerabilities
- 9.1 Critical severity
- 7.1 High severity
- 8.1 High severity
- 7.3 High severity
- 7.5 High severity
- 9.8 Critical severity
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