Sandbox escape due to incorrect boundary conditions in the Graphics: CanvasWebGL component.
CVE-2026-0878 is a high-severity improper input validation vulnerability in Firefox from Mozilla, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. There is no confirmed exploitation so far. EPSS estimates a 0.47% 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 Firefox you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on mozilla.org 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.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
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
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- 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:R/S:U/C:H/I:H/A:H. Scored by CNA.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 8.0 | High | CISA (ADP) |
| CVSS 3.1 | 7.5 | High | CNA |
Official description
Sandbox escape due to incorrect boundary conditions in the Graphics: CanvasWebGL component. This vulnerability was fixed in Firefox 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Input Validation
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
How developers prevent this class of flaw
- Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build recognizers for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses.
- Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
- Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
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
Other references
- bugzilla.mozilla.org/show_bug.cgi?id=2003989Permissions Required
- access.redhat.com/errata/RHSA-2026:0667
- access.redhat.com/errata/RHSA-2026:0694
- access.redhat.com/errata/RHSA-2026:0924
- access.redhat.com/errata/RHSA-2026:1320
- access.redhat.com/errata/RHSA-2026:1413
- access.redhat.com/errata/RHSA-2026:1414
- access.redhat.com/errata/RHSA-2026:1415
- access.redhat.com/errata/RHSA-2026:1461
- access.redhat.com/errata/RHSA-2026:1462
- access.redhat.com/errata/RHSA-2026:1471
- access.redhat.com/errata/RHSA-2026:1487
- access.redhat.com/errata/RHSA-2026:2041
- access.redhat.com/errata/RHSA-2026:2043
- access.redhat.com/errata/RHSA-2026:2044
Other vulnerabilities in Firefox
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
Recent Improper Input Validation vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 7.2 High severity
- 8.6 High severity
- 8.6 High severity
- 8.6 High severity
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