CVE-2020-7039: tcp_emu in tcp_subr.c in libslirp 4.1.0, as used in QEMU 4.2.0, mismanages memory, as demonstrated by IRC DCC

This month

MEDIUM 5.6REMOTEWATCHLISTDOWNGRADEDOWNGRADEMITIGATE

CVE-2020-7039 is a medium-severity flaw (CVSS 5.6) affecting libslirp, qemu, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

tcp_emu in tcp_subr.c in libslirp 4.1.0, as used in QEMU 4.2.0, mismanages memory, as demonstrated by IRC DCC commands in EMU_IRC. This can cause a heap-based buffer overflow or other out-of-bounds access which can lead to a DoS or potential execute arbitrary code.

Why this priority

Remotely exploitable, no login, no user action
On your watchlist

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

Risk facts

CVSS score	5.6 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	3.6% (top 11%)
CISA exploited list	No
Weakness	CWE-787
Published	2020-01-16
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: debian · libslirp project · opensuse · qemu

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

Am I affected?

Timeline

2020-01-16 23:15 UTCPublished CVE record published
2026-06-17 03:24 UTCUpdated Record last modified

libslirp project libslirp DOWNGRADE

Affected: 4.1.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.1.0

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 4.1.0 (Debian / Ubuntu)

apt-cache madison libslirp sudo apt install libslirp=<VERSION_BEFORE_4.1.0> sudo apt-mark hold libslirp

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

dnf --showduplicates list libslirp sudo dnf downgrade libslirp-<VERSION_BEFORE_4.1.0> sudo dnf versionlock add libslirp

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.

qemu qemu DOWNGRADE

Affected: 4.2.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.2.0

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 4.2.0 (Debian / Ubuntu)

apt-cache madison qemu sudo apt install qemu=<VERSION_BEFORE_4.2.0> sudo apt-mark hold qemu

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

dnf --showduplicates list qemu sudo dnf downgrade qemu-<VERSION_BEFORE_4.2.0> sudo dnf versionlock add qemu

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.

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.

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-2020-7039?

libslirp: downgrade or apply the listed mitigation; qemu: downgrade or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-7039 being exploited?

CVE-2020-7039 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-2020-7039 affect?

CVE-2020-7039 affects libslirp, qemu, debian linux. Severity is medium (CVSS 5.6). tcp_emu in tcp_subr.c in libslirp 4.1.0, as used in QEMU 4.2.0, mismanages memory, as demonstrated by IRC DCC commands in EMU_IRC. This can cause a heap-based buffer overflow or other out-of-bounds access which can lead to a DoS or potentia

How urgent is CVE-2020-7039?

Priority 52/100. Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities · QEMU vulnerabilities

Related CVEs

CVE-2021-3595 LOW 3.8 UPGRADE MITIGATE An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU
CVE-2021-3594 LOW 3.8 UPGRADE MITIGATE An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU
CVE-2021-3593 LOW 3.8 UPGRADE MITIGATE An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU
CVE-2021-3592 LOW 3.8 UPGRADE MITIGATE An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU
CVE-2020-8608 MEDIUM 5.6 DOWNGRADE MITIGATE In libslirp 4.1.0, as used in QEMU 4.2.0, tcp_subr.c misuses snprintf return values, leading to a buffer overf

References

← Back to latest CVEs