PaperCut NG/MF: Time-of-check Time-of-use (TOCTOU) Race Condition
CVE-2026-6180 is a high-severity time-of-check time-of-use (TOCTOU) race condition vulnerability in PaperCut NG/MF from PaperCut, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 24.1.9, 25.0.10 as the first without the flaw, so updating PaperCut NG/MF to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.34% 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
- Update PaperCut NG/MF to 24.1.9 or 25.0.10, whichever matches your release line, or a later version.
- Update Papercut Mf to 24.1.9 or 25.0.10, whichever matches your release line, or a later version.
- Update Papercut Ng to 24.1.9 or 25.0.10, whichever matches your release line, or a later version.
- Read the advisory on papercut.com for workarounds and exact fixed builds.
- 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 |
|---|---|---|---|
| PaperCut | PaperCut NG/MF | before 24.1.9; before 25.0.10 | 24.1.9, 25.0.10 |
| Papercut | Papercut Mf | before 24.1.9; 25.0.2 up to, but not including, 25.0.10 | 24.1.9, 25.0.10 |
| Papercut | Papercut Ng | before 24.1.9; 25.0.2 up to, but not including, 25.0.10 | 24.1.9, 25.0.10 |
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
- HighSuccess depends on conditions outside the attacker's control.
- 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
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 4.1 | Medium | CNA |
| CVSS 3.1 | 8.1 | High | NVD |
Official description
A race condition exists in PaperCut MF when processing badge-swipe data from certain HP multifunction devices. Under specific network conditions involving dropped packets and out-of-order sequence counters, the server may incorrectly process fragmented data chunks. If a sequence reset notification fails to reach the server, the server may reject the initial data chunk while erroneously accepting subsequent chunks before a connection reset completes. This leads to the registration of a truncated badge ID string. While this typically results in an authentication failure, the vulnerability is compounded in environments utilizing custom badge-ID post-processing scripts. In such configurations, the truncated string may be transformed into a valid ID belonging to a different user, leading to unauthorized session establishment (Incorrect User Login) on the device.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Time-of-check Time-of-use (TOCTOU) Race Condition
The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.
How developers prevent this class of flaw
- The most basic advice for TOCTOU vulnerabilities is to not perform a check before the use. This does not resolve the underlying issue of the execution of a function on a resource whose state and identity cannot be assured, but it does help to limit the false sense of security given by the check.
- When the file being altered is owned by the current user and group, set the effective gid and uid to that of the current user and group when executing this statement.
- Limit the interleaving of operations on files from multiple processes.
More Time-of-check Time-of-use (TOCTOU) Race Condition vulnerabilities (CWE-367)
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
Other vulnerabilities in PaperCut NG/MF
- 7.3 High severity
- 7.5 High severity
- 7.5 High severity
- 8.8 High severity
Recent Time-of-check Time-of-use (TOCTOU) Race Condition vulnerabilities
- 7.0 High severity
- 7.8 High severity
- 7.8 High severity
- 7.0 High severity
- 8.8 High severity
- 8.2 High severity
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