CVE-2018-20311: Foxit Reader before 9.5, and PhantomPDF before 8.3.10 and 9.x before 9.5, has a proxyCPDFAction race condition

Q: How do I fix CVE-2018-20311?

phantompdf: upgrade to 8.3.10, 9.5; reader: upgrade to 9.5. Exact commands for each OS are on this page.

Q: Is CVE-2018-20311 being exploited?

CVE-2018-20311 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2018-20311 affect?

CVE-2018-20311 affects phantompdf, reader. Severity is high (CVSS 8.1). Foxit Reader before 9.5, and PhantomPDF before 8.3.10 and 9.x before 9.5, has a proxyCPDFAction race condition that can cause a stack-based buffer overflow or an out-of-bounds read.

Q: How urgent is CVE-2018-20311?

Priority 48/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 8.1REMOTEUPGRADEUPGRADE

CVE-2018-20311 is a high-severity flaw (CVSS 8.1) affecting phantompdf, reader. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Foxit Reader before 9.5, and PhantomPDF before 8.3.10 and 9.x before 9.5, has a proxyCPDFAction race condition that can cause a stack-based buffer overflow or an out-of-bounds read.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.8% (top 43%)
CISA exploited list	No
Weakness	CWE-125, CWE-362, CWE-787
Published	2021-01-07
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: foxitsoftware

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-01-07 17:15 UTCPublished CVE record published
2026-06-17 01:52 UTCUpdated Record last modified

foxitsoftware phantompdf UPGRADE

Affected: < 8.3.10 · >= 9.0 and < 9.5

Fixed in: 8.3.10, 9.5

Safe to downgrade to: a release before 9.0

1. Check installed version

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

2. UPGRADE to 8.3.10 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade phantompdf

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade phantompdf

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 9.0 (Debian / Ubuntu)

apt-cache madison phantompdf sudo apt install phantompdf=<VERSION_BEFORE_9.0> sudo apt-mark hold phantompdf

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list phantompdf sudo dnf downgrade phantompdf-<VERSION_BEFORE_9.0> sudo dnf versionlock add phantompdf

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.

foxitsoftware reader UPGRADE

Affected: < 9.5

Fixed in: 9.5

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 9.5 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade reader

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade reader

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2018-20311?

phantompdf: upgrade to 8.3.10, 9.5; reader: upgrade to 9.5. Exact commands for each OS are on this page.

Is CVE-2018-20311 being exploited?

CVE-2018-20311 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-2018-20311 affect?

CVE-2018-20311 affects phantompdf, reader. Severity is high (CVSS 8.1). Foxit Reader before 9.5, and PhantomPDF before 8.3.10 and 9.x before 9.5, has a proxyCPDFAction race condition that can cause a stack-based buffer overflow or an out-of-bounds read.

How urgent is CVE-2018-20311?

Priority 48/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2022-25641 MEDIUM 5.5 UPGRADE UPGRADE Foxit PDF Reader before 11.2.2 and PDF Editor before 11.2.2, and PhantomPDF before 10.1.8, mishandle cross-ref
CVE-2021-41785 HIGH 7.8 UPGRADE UPGRADE Foxit PDF Reader before 11.1 and PDF Editor before 11.1, and PhantomPDF before 10.1.6, allow attackers to trig
CVE-2021-41784 HIGH 7.8 UPGRADE UPGRADE Foxit PDF Reader before 11.1 and PDF Editor before 11.1, and PhantomPDF before 10.1.6, allow attackers to trig
CVE-2021-41783 HIGH 7.8 UPGRADE UPGRADE Foxit PDF Reader before 11.1 and PDF Editor before 11.1, and PhantomPDF before 10.1.6, allow attackers to trig
CVE-2021-41782 HIGH 7.8 UPGRADE UPGRADE Foxit PDF Reader before 11.1 and PDF Editor before 11.1, and PhantomPDF before 10.1.6, allow attackers to trig

References

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