CVE-2008-5523: avast! antivirus 4.8.1281.0, when Internet Explorer 6 or 7 is used, allows remote attackers to bypass detectio

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HIGH 9.3DOWNGRADE

CVE-2008-5523 is a high-severity flaw (CVSS 9.3) affecting avast antivirus. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

avast! antivirus 4.8.1281.0, when Internet Explorer 6 or 7 is used, allows remote attackers to bypass detection of malware in an HTML document by placing an MZ header (aka "EXE info") at the beginning, and modifying the filename to have (1) no extension, (2) a .txt extension, or (3) a .jpg extension, as demonstrated by a document containing a CVE-2006-5745 exploit.

Why this priority

Critical severity

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.3 (High)
EPSS exploit chance	2.9% (top 13%)
CISA exploited list	No
Weakness	CWE-20
Published	2008-12-12
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: avast

Last updated 2026-06-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2008-12-12 18:30 UTCPublished CVE record published
2026-06-16 23:00 UTCUpdated Record last modified

avast avast antivirus DOWNGRADE

Affected: 4.8.1281.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.8.1281.0

1. Check installed version

apt-cache policy avast-antivirus || rpm -q avast-antivirus || avast-antivirus --version

2. No fixed release: DOWNGRADE to a release before 4.8.1281.0 (Debian / Ubuntu)

apt-cache madison avast-antivirus sudo apt install avast-antivirus=<VERSION_BEFORE_4.8.1281.0> sudo apt-mark hold avast-antivirus

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list avast-antivirus sudo dnf downgrade avast-antivirus-<VERSION_BEFORE_4.8.1281.0> sudo dnf versionlock add avast-antivirus

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2008-5523?

avast antivirus: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2008-5523 being exploited?

CVE-2008-5523 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2008-5523 affect?

CVE-2008-5523 affects avast antivirus. Severity is high (CVSS 9.3). avast! antivirus 4.8.1281.0, when Internet Explorer 6 or 7 is used, allows remote attackers to bypass detection of malware in an HTML document by placing an MZ header (aka "EXE info") at the beginning, and modifying the filename to have (1)

How urgent is CVE-2008-5523?

Priority 54/100. Critical severity

Software pages

Internet Explorer vulnerabilities

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References

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