An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU. The flaw exists in the udp6_input() function and could occur while processing a udp packet that is smaller than the size of the 'udphdr' structure. This issue may lead to out-of-bounds read access or indirect host memory disclosure to the guest. The highest threat from this vulnerability is to data confidentiality. This flaw affects libslirp versions prior to 4.6.0.
Conclusion & alert: CVE-2021-3593 is rated Low Risk (17.6/100): CVSS Low severity, with low exploitation likelihood (EPSS 0.03%). Mandatory action: Low composite risk—no urgent action required; patch on your normal maintenance cycle and revisit priority if CVSS or EPSS increases.
Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.
EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).
| # | Date | Old EPSS score | New EPSS score | Delta (New - Old) |
|---|---|---|---|---|
| 1 | 2025-11-21 | 0.07% | 0.03% | -0.04% |
| 2 | 2025-11-18 | 0.05% | 0.07% | +0.02% |
| 3 | 2023-03-07 | — | 0.05% | — |
Full EPSS history (11 records total)
CVSS metrics for this CVE.
| Base score | Version | Severity | Vector | Exploitability | Impact | Score source |
|---|---|---|---|---|---|---|
| 3.8 | 3.1 | LOW |
|
2.0 | 1.4 | [email protected] |
| 2.1 | 2.0 | LOW |
|
3.9 | 2.9 | [email protected] |
| vendor | priority | summary | link |
|---|---|---|---|
alpine
|
low | CVE-2021-3593: 1 source package rows (libslirp); 13 state rows across 7 repos (3.17-community, 3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community); fixed 7, open 6. | https://security.alpinelinux.org/vuln/CVE-2021-3593 |
debian
|
not yet assigned | CVE-2021-3593 not yet assigned priority: Debian including 2 source packages (libslirp, qemu), 10 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 10. | https://security-tracker.debian.org/tracker/CVE-2021-3593 |
gentoo
|
low | CVE-2021-3593: 1 GLSA(s) (202107-44), 1 atom(s) (net-libs/libslirp); latest impact low. | https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-3593 |
redhat
|
low | — | https://access.redhat.com/security/cve/CVE-2021-3593 |
suse
|
low | CVE-2021-3593 severity low: SUSE including 461 source package names (1.2.3-2.2.63:libslirp0-4.3.1-150300.11.1, 1.2.3-3.2.78:libslirp0-4.3.1-150300.11.1, …), 970 product×package rows across 70 product lines (Container rancher/elemental-teal-iso/5.4, Container rancher/elemental-teal-rt/5.4, … (70 product lines)): Fixed 634, Known Affected 225, Known Not Affected 111. | https://www.suse.com/security/cve/CVE-2021-3593/ |
ubuntu
|
low | CVE-2021-3593 low priority: Ubuntu including 2 source packages (libslirp, qemu), 32 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): released 13, not-affected 12, DNE 2, needed 2, needs-triage 2, ignored 1. | https://ubuntu.com/security/CVE-2021-3593 |
| Vendor | Product | Version | Raw CPE |
|---|---|---|---|
| libslirp_project | libslirp | < 4.6.0 | cpe:2.3:a:libslirp_project:libslirp:*:*:*:*:*:*:*:* |
| redhat | enterprise_linux | 8.0 | cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:* |
| redhat | enterprise_linux | 8.0 | cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:advanced_virtualization:*:*:* |
| fedoraproject | fedora | 33 | cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:* |
| fedoraproject | fedora | 34 | cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:* |
| debian | debian_linux | 9.0 | cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:* |