In Avast Antivirus before 19.4, a local administrator can trick the product into renaming arbitrary files by replacing the Logs\Update.log f
In Avast Antivirus before 19.4, a local administrator can trick the product into renaming arbitrary files by replacing the Logs\Update.log file with a symlink. The next time the product attempts to write to the log file, the target of the symlink is renamed. This defect can be exploited to rename a critical product file (e.g., AvastSvc.exe), causing the product to fail to start on the next system restart.
- Published
- Jul 18, 2019
- Updated
- Jun 16, 2026
- EPSS
- 0.5% · 44th percentile
- CWE
- CWE-59
Sign in to follow · You’ll be notified if a followed record enters KEV, gets an exploit or is updated.
Report tools
Action score
17
Monitor
Low priority for now.
- CVSS
- 17 / 40 · 4.4 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.5%
Noroxi analysis
No Noroxi analysis for this record yet
We don't hand-write analysis for the hundreds of thousands of vulnerabilities in the database; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.
We use this product, ask for helpAffected systems
| Vendor | Product | CPE |
|---|---|---|
| avast | antivirus | cpe:2.3:a:avast:antivirus |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- avast antivirusbefore 19.4
Same product
avast: all recordsOther highest-scoring records for the same primary product.
- CVE-2020-10867An issue was discovered in Avast Antivirus before 20.40Plan
- CVE-2017-8307In Avast Antivirus before v17, using the LPC interface API exposed by the AvastSVC.exe Windows service, it is possible to launch predefined 40Plan
- CVE-2025-3500Integer Overflow in Avast Antiviurs 25.1.981.6 on Windows may result in privilege escalation39Monitor
- CVE-2021-45337Privilege escalation vulnerability in the Self-Defense driver of Avast Antivirus prior to 20.8 allows a local user with SYSTEM privileges to35Monitor
- CVE-2021-45336Privilege escalation vulnerability in the Sandbox component of Avast Antivirus prior to 20.4 allows a local sandboxed code to gain elevated 35Monitor
- CVE-2021-45335Sandbox component in Avast Antivirus prior to 20.4 has an insecure permission which could be abused by local user to control the outcome of 35Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
No fix version is recorded for this entry. Check the references for vendor advisories.
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Someone with local access to the system can trigger it.
- Administrator privileges are required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- none
- Integrity
- high · data or configuration can be modified
- Availability
- none
- Attack vector
- Local
- Attack complexity
- Low
- Privileges required
- High
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- High
- Availability impact
- None
Weakness class (CWE)
CWE-59 · Improper Link Resolution Before File Access ('Link Following')CVSS vector
CVSS:3.0/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
ATT&CK techniques
- Obfuscated Files or Information: HTML SmugglingT1027.006
- Obfuscated Files or Information: Embedded PayloadsT1027.009
- Boot or Logon Autostart Execution:Shortcut ModificationT1547.009
- Hide Artifacts: Resource ForkingT1564.009
- Hijack Execution Flow: Executable Installer File Permissions WeaknessT1574.005
- Hijack Execution Flow: Services File Permissions WeaknessT1574.010
Change log
No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.
References
Vendor advisories and official records. Exploit/PoC links are deliberately left out.