CVE-2020-1983Public exploitNetwork attack vector

Host-process crash via stale reassembly pointer

Published Apr 22, 2020 · Updated Sep 16, 2024

Use after free in Libslirp Project libslirp 4.2.0 and earlier allows remote attackers to crash its host process with crafted packets. During IP fragment reassembly, m_cat() can reallocate and move an mbuf's external buffer, but ip_reass() continues using the stale q pointer. The attack requires packet reachability to a libslirp-backed virtual network; published evidence demonstrates process interruption, not data access.

CVSS severity7.5
High
EPSS probability2.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use after free in Libslirp Project libslirp 4.2.0 and earlier allows remote attackers to crash its host process with crafted packets. During IP fragment reassembly, m_cat() can reallocate and move an mbuf's external buffer, but ip_reass() continues using the stale q pointer. The attack requires packet reachability to a libslirp-backed virtual network; published evidence demonstrates process interruption, not data access.

The record

CVE
CVE-2020-1983
Published
Apr 22, 2020
Updated
Sep 16, 2024
Vendor
Libslirp Project
Product
libslirp
Classifications
CWE-416, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 2020CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <=4.2.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Libslirp Project · libslirpversion=unspecified <=4.2.0

Published CVSS scores

7.5Palo Alto NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
6.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-416Use After Free
T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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