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Fencer Vulns
high 7.5

CVE-2019-18840 json

In wolfSSL 4.1.0 through 4.2.0c, there are missing sanity checks of memory accesses in parsing ASN.1 certificate data while handshaking.

published 2019-11-09 7 y ago modified 2026-06-17 4 mo ago also EUVD-2019-8541

cvss
7.5
version 3.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.0%
EPSS 2.0% chance of exploitation in 30 days, percentile 80%
public exploits
0
none known

Summary

In wolfSSL 4.1.0 through 4.2.0c, there are missing sanity checks of memory accesses in parsing ASN.1 certificate data while handshaking. Specifically, there is a one-byte heap-based buffer overflow inside the DecodedCert structure in GetName in wolfcrypt/src/asn.c because the domain name location index is mishandled. Because a pointer is overwritten, there is an invalid free.

Patch / fix

  • wolfssl Debian 13, Debian 12 4.2.0+dfsg-3

debian advisories DEBIAN-CVE-2019-18840

  • wolfssl Ubuntu 20.04 LTS 4.2.0+dfsg-3

ubuntu advisories UBUNTU-CVE-2019-18840

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Exploit prediction

1.97% chance of exploitation in the next 30 days, higher than 80% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/wolfSSL/wolfssl/issues/2555 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.0 7.5 CVSS:3.0/AC:L/AV:N/A:H/C:N/I:N/PR:N/S:U/UI:N
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 3.0 7.5 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.