CVE-2011-1331: JustSystems Ichitaro 2005 through 2011, Ichitaro Government 6, Ichitaro Government 2006 through 2010, Ichitaro

This week

HIGH 9.3DOWNGRADEMITIGATEMITIGATE

CVE-2011-1331 is a high-severity flaw (CVSS 9.3) affecting ichitaro, ichitaro portable, ichitaro pro. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

JustSystems Ichitaro 2005 through 2011, Ichitaro Government 6, Ichitaro Government 2006 through 2010, Ichitaro Portable, Ichitaro Pro, and Ichitaro Viewer allow remote attackers to execute arbitrary code or cause a denial of service (heap memory corruption) via a crafted document, as exploited in the wild in early 2011.

Why this priority

Critical severity
EPSS top 7%: very likely to be exploited
Public exploit reference

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

Risk facts

CVSS score	9.3 (High)
EPSS exploit chance	5.6% (top 7%)
CISA exploited list	No
Weakness	CWE-119
Published	2011-07-18
Last modified	2026-06-16

Publisher (CNA): JPCERT/CC · Vendor: justsystems

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

Am I affected?

Timeline

2011-07-18 22:55 UTCPublished CVE record published
2026-06-16 23:29 UTCUpdated Record last modified

justsystems ichitaro DOWNGRADE

Affected: 6 · 2005 · 2006 · 2007 · 2008 · 2009 · 2010 · 2011

Fixed in: no fixed release known

Safe to downgrade to: a release before 6

1. Check installed version

apt-cache policy ichitaro || rpm -q ichitaro || ichitaro --version

2. No fixed release: DOWNGRADE to a release before 6 (Debian / Ubuntu)

apt-cache madison ichitaro sudo apt install ichitaro=<VERSION_BEFORE_6> sudo apt-mark hold ichitaro

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

dnf --showduplicates list ichitaro sudo dnf downgrade ichitaro-<VERSION_BEFORE_6> sudo dnf versionlock add ichitaro

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.

justsystems ichitaro portable MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy ichitaro-portable || rpm -q ichitaro-portable || ichitaro-portable --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

justsystems ichitaro pro MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy ichitaro-pro || rpm -q ichitaro-pro || ichitaro-pro --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

justsystems ichitaro viewer DOWNGRADE

Affected: all versions · 5.1.3.0 · 19.0.1.0 · 19.0.2.0 · 19.0.3.0 · 20.0.2.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.1.3.0

1. Check installed version

apt-cache policy ichitaro-viewer || rpm -q ichitaro-viewer || ichitaro-viewer --version

2. No fixed release: DOWNGRADE to a release before 5.1.3.0 (Debian / Ubuntu)

apt-cache madison ichitaro-viewer sudo apt install ichitaro-viewer=<VERSION_BEFORE_5.1.3.0> sudo apt-mark hold ichitaro-viewer

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

dnf --showduplicates list ichitaro-viewer sudo dnf downgrade ichitaro-viewer-<VERSION_BEFORE_5.1.3.0> sudo dnf versionlock add ichitaro-viewer

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-2011-1331?

ichitaro: downgrade or apply the listed mitigation; ichitaro portable: mitigate or apply the listed mitigation; ichitaro pro: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2011-1331 being exploited?

CVE-2011-1331 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-2011-1331 affect?

CVE-2011-1331 affects ichitaro, ichitaro portable, ichitaro pro. Severity is high (CVSS 9.3). JustSystems Ichitaro 2005 through 2011, Ichitaro Government 6, Ichitaro Government 2006 through 2010, Ichitaro Portable, Ichitaro Pro, and Ichitaro Viewer allow remote attackers to execute arbitrary code or cause a denial of service (heap m

How urgent is CVE-2011-1331?

Priority 61/100. Critical severity; EPSS top 7%: very likely to be exploited; Public exploit reference

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References

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