CVE-2020-1983: A use after free vulnerability in ip_reass() in ip_input.c of libslirp 4.2.0 and prior releases allows crafted

Q: How do I fix CVE-2020-1983?

libslirp: upgrade to newer than 4.2.0; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2020-1983 being exploited?

CVE-2020-1983 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-2020-1983 affect?

CVE-2020-1983 affects libslirp, fedora, debian linux. Severity is high (CVSS 7.5). A use after free vulnerability in ip_reass() in ip_input.c of libslirp 4.2.0 and prior releases allows crafted packets to cause a denial of service.

Q: How urgent is CVE-2020-1983?

Priority 62/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

This week

HIGH 7.5REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2020-1983 is a high-severity flaw (CVSS 7.5) affecting libslirp, fedora, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A use after free vulnerability in ip_reass() in ip_input.c of libslirp 4.2.0 and prior releases allows crafted packets to cause a denial of service.

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.4% (top 16%)
CISA exploited list	No
Weakness	CWE-416
Published	2020-04-22
Last modified	2026-06-17

Publisher (CNA): Palo Alto Networks, Inc. · Vendor: canonical · debian · fedoraproject · libslirp project · opensuse

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

Am I affected?

Timeline

2020-04-22 20:15 UTCPublished CVE record published
2026-06-17 03:02 UTCUpdated Record last modified

libslirp project libslirp UPGRADE

Affected: <= 4.2.0

Fixed in: newer than 4.2.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to newer than 4.2.0 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade libslirp

Note

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

fedoraproject fedora MITIGATE

Affected: 31 · 32

Fixed in: no fixed release known

Safe to downgrade to: a release before 31

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

debian debian linux MITIGATE

Affected: 8.0 · 9.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

opensuse leap MITIGATE

Affected: 15.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 15.1

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

canonical ubuntu linux MITIGATE

Affected: 16.04 · 18.04 · 19.10 · 20.04

Fixed in: no fixed release known

Safe to downgrade to: a release before 16.04

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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-2020-1983?

libslirp: upgrade to newer than 4.2.0; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-1983 being exploited?

CVE-2020-1983 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-2020-1983 affect?

CVE-2020-1983 affects libslirp, fedora, debian linux. Severity is high (CVSS 7.5). A use after free vulnerability in ip_reass() in ip_input.c of libslirp 4.2.0 and prior releases allows crafted packets to cause a denial of service.

How urgent is CVE-2020-1983?

Priority 62/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Ubuntu vulnerabilities · Debian vulnerabilities

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References

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