CVE-2020-29129: ncsi.c in libslirp through 4.3.1 has a buffer over-read because it tries to read a certain amount of header da

Q: How do I fix CVE-2020-29129?

libslirp: upgrade to newer than 4.3.1; 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-2020-29129 being exploited?

CVE-2020-29129 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-2020-29129 affect?

CVE-2020-29129 affects libslirp, fedora, debian linux. Severity is medium (CVSS 4.3). ncsi.c in libslirp through 4.3.1 has a buffer over-read because it tries to read a certain amount of header data even if that exceeds the total packet length.

Q: How urgent is CVE-2020-29129?

Priority 38/100. On your watchlist

Routine

MEDIUM 4.3WATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2020-29129 is a medium-severity flaw (CVSS 4.3) affecting libslirp, fedora, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

ncsi.c in libslirp through 4.3.1 has a buffer over-read because it tries to read a certain amount of header data even if that exceeds the total packet length.

Why this priority

On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.5% (top 26%)
CISA exploited list	No
Weakness	CWE-125
Published	2020-11-26
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: debian · fedoraproject · libslirp project

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

Am I affected?

Timeline

2020-11-26 20:15 UTCPublished CVE record published
2026-06-17 03:11 UTCUpdated Record last modified

libslirp project libslirp UPGRADE

Affected: <= 4.3.1

Fixed in: newer than 4.3.1

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 4.3.1 (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: 32 · 33

Fixed in: no fixed release known

Safe to downgrade to: a release before 32

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: 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 10.0

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.

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-2020-29129?

libslirp: upgrade to newer than 4.3.1; 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-2020-29129 being exploited?

CVE-2020-29129 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-2020-29129 affect?

CVE-2020-29129 affects libslirp, fedora, debian linux. Severity is medium (CVSS 4.3). ncsi.c in libslirp through 4.3.1 has a buffer over-read because it tries to read a certain amount of header data even if that exceeds the total packet length.

How urgent is CVE-2020-29129?

Priority 38/100. On your watchlist

Software pages

Debian vulnerabilities

Related CVEs

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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

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