- Exploited
- No known exploitation
- Fix
- Fixed in 26.7
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 26.7.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 0/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Avast's Windows Filtering Platform stream parser on Windows contains an integer underflow that can be triggered by specially crafted network traffic or local input, causing a system crash. An attacker can use it to cause denial of service, not to gain control of the system.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
An integer underflow vulnerability in the Avast Windows Filtering Platform (WFP) stream parser on Windows allows denial of service by causing a system crash.
The WFP callout driver processes network stream data and computes length values for packet fragment reassembly. The length calculation does not properly validate input stream sizes against expected boundaries. When processing specially crafted input, the length computation underflows, resulting in allocation or buffer access with an extremely large wrapped-around size value.
The underflow can be triggered remotely via network traffic destined for the filtered port, or locally via crafted data provided to the filtering interface. The resulting memory allocation failure or out-of-bounds access causes a kernel panic and system crash.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure?/25Unknown. No advisory context yet
- Reach?/20Unknown. No tracked technology or package matched
- Severity?/10Unknown. No CVSS score or vendor rating
- No patch0/5No signal
What would change the score
- Would score about 55 if added to CISA KEV
- Would score about 50 if CISA's SSVC rates exploitation active
- Would score about 22 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 26.7.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- Gen Digital Avast Antivirus, Avast One, Avast Premium Security, Avast Ultimate
fixed in 26.7
- Gen Digital AVG Antivirus Free, AVG Internet Security, AVG Ultimate
fixed in 26.7
- Gen Digital Norton Antivirus Plus, Norton 360 Standard, Norton 360 Deluxe, Norton 360 Advanced
fixed in 26.7
Evidence 4
- Advisory
- Patch
- Patch
- Patch
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-80303
Is CVE-2026-80303 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-80303?
Avast Antivirus, Avast One, Avast Premium Security, Avast Ultimate: before 26.7. AVG Antivirus Free, AVG Internet Security, AVG Ultimate: before 26.7. Norton Antivirus Plus, Norton 360 Standard, Norton 360 Deluxe, Norton 360 Advanced: before 26.7.Source: cve.now feed data
How do I fix CVE-2026-80303?
Upgrade to a fixed version: 26.7.Source: cve.now feed data