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CVE-2020-1983· NVD / CVE Program· CNA palo_alto

libslirp: use after free vulnerability cause a denial of service.

Noroxi assessment

Priority: Monitor (action score 27/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 2.3% (FIRST EPSS); higher than 83.2% of all records.
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: hivex (AlmaLinux:8) 1.3.18-20.module_el8.3.0+2048+e7a0a3ea; hivex-devel (AlmaLinux:8) 1.3.18-20.module_el8.3.0+2048+e7a0a3ea; libguestfs-winsupport (AlmaLinux:8) 8.2-1.module_el8.5.0+2608+72063365, 8.2-1.module_el8.3.0+2048+e7a0a3ea.
  • Mentioned 2 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to hivex (AlmaLinux:8) 1.3.18-20.module_el8.3.0+2048+e7a0a3ea; hivex-devel (AlmaLinux:8) 1.3.18-20.module_el8.3.0+2048+e7a0a3ea; libguestfs-winsupport (AlmaLinux:8) 8.2-1.module_el8.5.0+2608+72063365, 8.2-1.module_el8.3.0+2048+e7a0a3ea or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

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.

MediumCVSS 6.5 · v3.1—No exploit Fix available
Published
Apr 22, 2020
Updated
Jun 16, 2026
EPSS
2.4% · 83th percentile

Report tools

JSON

Action score

27

Monitor

Low priority for now.

CVSS
26 / 40 · 6.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
1 / 30 · 2.4%

CNA vs NVD score

NVD
6.5
CNA · palo_alto
7.5
1.0 point gap

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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When you'll hear from us

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  • when exploit code appears or is weaponized
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  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
libslirp projectlibslirp
fedoraprojectfedora
debiandebian linux
opensuseleap
canonicalubuntu linux

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • canonical ubuntu linux16.04
  • canonical ubuntu linux18.04
  • canonical ubuntu linux19.10
  • canonical ubuntu linux20.04
  • debian debian linux8.0
  • debian debian linux9.0
  • fedoraproject fedora31
  • fedoraproject fedora32
  • libslirp project libslirpup to 4.2.0 inclusive
  • opensuse leap15.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (palo_alto). Independent of NVD's CPE analysis and usually ahead of it.

  • slirp libslirp

    • unspecified and later · up to and including 4.2.0affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:8hivexbefore 1.3.18-20.module_el8.3.0+2048+e7a0a3ea1.3.18-20.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8hivex-develbefore 1.3.18-20.module_el8.3.0+2048+e7a0a3ea1.3.18-20.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libguestfs-winsupportbefore 8.2-1.module_el8.5.0+2608+720633658.2-1.module_el8.5.0+2608+72063365
AlmaLinux:8libguestfs-winsupportbefore 8.2-1.module_el8.3.0+2048+e7a0a3ea8.2-1.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libiscsibefore 1.18.0-8.module_el8.5.0+2608+720633651.18.0-8.module_el8.5.0+2608+72063365
AlmaLinux:8libiscsibefore 1.18.0-8.module_el8.6.0+2880+7d9e37031.18.0-8.module_el8.6.0+2880+7d9e3703
AlmaLinux:8libiscsibefore 1.18.0-8.module_el8.3.0+2048+e7a0a3ea1.18.0-8.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libiscsi-develbefore 1.18.0-8.module_el8.6.0+2880+7d9e37031.18.0-8.module_el8.6.0+2880+7d9e3703
AlmaLinux:8libiscsi-develbefore 1.18.0-8.module_el8.5.0+2608+720633651.18.0-8.module_el8.5.0+2608+72063365
AlmaLinux:8libiscsi-develbefore 1.18.0-8.module_el8.3.0+2048+e7a0a3ea1.18.0-8.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libiscsi-utilsbefore 1.18.0-8.module_el8.3.0+2048+e7a0a3ea1.18.0-8.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libiscsi-utilsbefore 1.18.0-8.module_el8.6.0+2880+7d9e37031.18.0-8.module_el8.6.0+2880+7d9e3703
AlmaLinux:8libiscsi-utilsbefore 1.18.0-8.module_el8.5.0+2608+720633651.18.0-8.module_el8.5.0+2608+72063365
AlmaLinux:8libnbdbefore 1.2.2-1.module_el8.5.0+2608+720633651.2.2-1.module_el8.5.0+2608+72063365
AlmaLinux:8libnbdbefore 1.2.2-1.module_el8.3.0+2048+e7a0a3ea1.2.2-1.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libnbd-develbefore 1.2.2-1.module_el8.3.0+2048+e7a0a3ea1.2.2-1.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libnbd-develbefore 1.2.2-1.module_el8.5.0+2608+720633651.2.2-1.module_el8.5.0+2608+72063365
AlmaLinux:8libvirtbefore 6.0.0-28.module_el8.3.0+2048+e7a0a3ea6.0.0-28.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libvirt-adminbefore 6.0.0-28.module_el8.3.0+2048+e7a0a3ea6.0.0-28.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libvirt-bash-completionbefore 6.0.0-28.module_el8.3.0+2048+e7a0a3ea6.0.0-28.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libvirt-clientbefore 6.0.0-28.module_el8.3.0+2048+e7a0a3ea6.0.0-28.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libvirt-daemonbefore 6.0.0-28.module_el8.3.0+2048+e7a0a3ea6.0.0-28.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libvirt-daemon-config-networkbefore 6.0.0-28.module_el8.3.0+2048+e7a0a3ea6.0.0-28.module_el8.3.0+2048+e7a0a3ea
AlmaLinux:8libvirt-daemon-config-nwfilterbefore 6.0.0-28.module_el8.3.0+2048+e7a0a3ea6.0.0-28.module_el8.3.0+2048+e7a0a3ea

+96

Same product

libslirp project: all records

Other highest-scoring records for the same primary product.

  • CVE-2019-14378ip_reass in ip_input.c in libslirp 4.0.0 has a heap-based buffer overflow via a large packet because it mishandles a case involving the firs
    40Plan
  • CVE-2020-10756An out-of-bounds read vulnerability was found in the SLiRP networking implementation of the QEMU emulator.
    26Monitor
  • CVE-2020-8608In libslirp 4.1.0, as used in QEMU 4.2.0, tcp_subr.c misuses snprintf return values, leading to a buffer overflow in later code.
    23Monitor
  • CVE-2020-29130slirp.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 t
    18Monitor
  • CVE-2020-29129ncsi.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 to
    17Monitor
  • CVE-2021-3595An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU.
    15Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
almalinux:hivex1.3.18-20.module_el8.3.0+2048+e7a0a3ea · AlmaLinux:8Package registry (OSV)
almalinux:hivex-devel1.3.18-20.module_el8.3.0+2048+e7a0a3ea · AlmaLinux:8Package registry (OSV)
almalinux:libguestfs-winsupport8.2-1.module_el8.5.0+2608+72063365 · AlmaLinux:8Package registry (OSV)
almalinux:libiscsi1.18.0-8.module_el8.6.0+2880+7d9e3703 · AlmaLinux:8Package registry (OSV)
almalinux:libiscsi-devel1.18.0-8.module_el8.6.0+2880+7d9e3703 · AlmaLinux:8Package registry (OSV)
almalinux:libiscsi-utils1.18.0-8.module_el8.3.0+2048+e7a0a3ea · AlmaLinux:8Package registry (OSV)
almalinux:libnbd1.2.2-1.module_el8.5.0+2608+72063365 · AlmaLinux:8Package registry (OSV)
almalinux:libnbd-devel1.2.2-1.module_el8.3.0+2048+e7a0a3ea · AlmaLinux:8Package registry (OSV)
almalinux:python-podman-api1.2.0-0.2.gitd0a45fe.module_el8.5.0+2635+e4386a39 · AlmaLinux:8Package registry (OSV)
almalinux:runc1.0.0-66.rc10.module_el8.5.0+2635+e4386a39 · AlmaLinux:8Package registry (OSV)
almalinux:toolbox0.0.7-1.module_el8.5.0+108+00865455 · AlmaLinux:8Package registry (OSV)
almalinux:udica0.2.1-2.module_el8.5.0+108+00865455 · AlmaLinux:8Package registry (OSV)
debian:libslirp4.2.0-2 · Debian:12Package registry (OSV)
debian:qemu1:4.1-2 · Debian:12Package registry (OSV)
debian:slirp4netns1.0.1-1 · Debian:12Package registry (OSV)
opensuse:libslirp4.6.1+7-1.2 · openSUSE:TumbleweedPackage registry (OSV)
opensuse:qemu3.1.1.1-lp151.7.15.2 · openSUSE:Leap 15.1Package registry (OSV)
opensuse:qemu-linux-user3.1.1.1-lp151.7.15.2 · openSUSE:Leap 15.1Package registry (OSV)
opensuse:slirp4netns0.4.5-lp151.2.9.1 · openSUSE:Leap 15.1Package registry (OSV)
red hat:hivex0:1.3.18-20.module+el8.2.0+5588+63a201c3 · Red Hat:advanced_virtualization:8.2::el8Package registry (OSV)
red hat:hivex-debuginfo0:1.3.18-20.module+el8.2.0+5588+63a201c3 · Red Hat:advanced_virtualization:8.2::el8Package registry (OSV)
red hat:hivex-debugsource0:1.3.18-20.module+el8.2.0+5588+63a201c3 · Red Hat:advanced_virtualization:8.2::el8Package registry (OSV)
red hat:hivex-devel0:1.3.18-20.module+el8.2.0+5588+63a201c3 · Red Hat:advanced_virtualization:8.2::el8Package registry (OSV)
red hat:libguestfs1:1.40.2-24.module+el8.2.1+7154+47ffd890 · Red Hat:advanced_virtualization:8.2::el8Package registry (OSV)
red hat:libguestfs-bash-completion1:1.40.2-24.module+el8.2.1+7154+47ffd890 · Red Hat:advanced_virtualization:8.2::el8Package registry (OSV)
red hat:libguestfs-benchmarking1:1.40.2-24.module+el8.2.1+7154+47ffd890 · Red Hat:advanced_virtualization:8.2::el8Package registry (OSV)
red hat:libguestfs-benchmarking-debuginfo1:1.40.2-24.module+el8.2.1+7154+47ffd890 · Red Hat:advanced_virtualization:8.2::el8Package registry (OSV)
red hat:libguestfs-debuginfo1:1.40.2-24.module+el8.2.1+7154+47ffd890 · Red Hat:advanced_virtualization:8.2::el8Package registry (OSV)
red hat:libguestfs-debugsource1:1.40.2-24.module+el8.2.1+7154+47ffd890 · Red Hat:advanced_virtualization:8.2::el8Package registry (OSV)
red hat:libguestfs-devel1:1.40.2-24.module+el8.2.1+7154+47ffd890 · Red Hat:advanced_virtualization:8.2::el8Package registry (OSV)

+16

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted

Impact can extend beyond the vulnerable component (scope changes).

Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H

nvd-primary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

c
free(dev->buf);/* ... another thread is still running ... */process(dev->buf);

Fixed

c
lock(&dev->lock);free(dev->buf);dev->buf = NULL;unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (8 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records