Apache ActiveMQ: Integer Overflow or Wraparound
CVE-2025-66168 is a high-severity integer overflow or wraparound vulnerability in Apache ActiveMQ from Apache, with a CVSS 3.1 base score of 8.8 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. The record lists versions 5.19.2, 6.1.9, 6.2.1 as the first without the flaw, so updating Apache ActiveMQ to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.87% chance of exploitation within 30 days, higher than 59% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Apache ActiveMQ to 5.19.2 or 6.1.9 or 6.2.1, whichever matches your release line, or a later version.
- Update Apache ActiveMQ All Module to 5.19.2 or 6.1.9 or 6.2.1, whichever matches your release line, or a later version.
- Update Apache ActiveMQ MQTT Module to 5.19.2 or 6.1.9 or 6.2.1, whichever matches your release line, or a later version.
- Read the advisory on activemq.apache.org for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Apache | Apache ActiveMQ | before 5.19.2; 6.0.0 up to, but not including, 6.1.9; 6.2.0 up to, but not including, 6.2.1 | 5.19.2, 6.1.9, 6.2.1 |
| Apache | Apache ActiveMQ All Module | before 5.19.2; 6.0.0 up to, but not including, 6.1.9; 6.2.0 up to, but not including, 6.2.1 | 5.19.2, 6.1.9, 6.2.1 |
| Apache | Apache ActiveMQ MQTT Module | before 5.19.2; 6.0.0 up to, but not including, 6.1.9; 6.2.0 up to, but not including, 6.2.1 | 5.19.2, 6.1.9, 6.2.1 |
| Apache | Activemq | before 5.19.2; 6.0.0 through 6.1.8; 6.2.0 | 5.19.2 |
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
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 5.4 | Medium | CNA (apache.org) |
| CVSS 3.1 | 8.8 | High | NVD |
Official description
WARNING: Users of 6.x should upgrade to 6.2.4 or later as the fix was missed in previous 6.x releases. See the following for more details: https://activemq.apache.org/security-advisories.data/CVE-2026-40046-announcement.txt https://www.cve.org/CVERecord?id=CVE-2026-40046 Original Report: Apache ActiveMQ does not properly validate the remaining length field which may lead to an overflow during the decoding of malformed packets. When this integer overflow occurs, ActiveMQ may incorrectly compute the total Remaining Length and subsequently misinterpret the payload as multiple MQTT control packets which makes the broker susceptible to unexpected behavior when interacting with non-compliant clients. This behavior violates the MQTT v3.1.1 specification, which restricts Remaining Length to a maximum of 4 bytes. The scenario occurs on established connections after the authentication process. Brokers that are not enabling mqtt transport connectors are not impacted. This issue affects Apache ActiveMQ: before 5.19.2, 6.0.0 to 6.1.8, and 6.2.0 Users are recommended to upgrade to version 5.19.2, 6.1.9, or 6.2.1, which fixes the issue.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Integer Overflow or Wraparound
The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
How developers prevent this class of flaw
- Ensure that all protocols are strictly defined, such that all out-of-bounds behavior can be identified simply, and require strict conformance to the protocol.
- Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. If possible, choose a language or compiler that performs automatic bounds checking.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Use libraries or frameworks that make it easier to handle numbers without unexpected consequences. Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++).
More Integer Overflow or Wraparound vulnerabilities (CWE-190)
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
Advisories
Third-party and government advisories
- openwall.com/lists/oss-security/2026/03/03/5Mailing List, Third Party Advisory
Other references
Other vulnerabilities in Apache ActiveMQ
- 8.1 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
Recent Integer Overflow or Wraparound vulnerabilities
- 8.8 High severity
- 8.4 High severity
- 8.4 High severity
- 7.8 High severity
- 9.1 Critical severity
- 7.5 High severity
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