CVE-2026-34873: trustedfirmware mbed_tls Improper Authentication
CVSS: 9.1v3.1CriticalAnalyzed
AliasesUBUNTU-CVE-2026-34873DEBIAN-CVE-2026-34873
Published 01-04-2026Last modified 02-04-2026
Vulnerability summary
CVE-2026-34873 is a critical (CVSS 9.1) Improper Authentication vulnerability in trustedfirmware mbed_tls. EPSS estimates a 0.42% chance of exploitation in the next 30 days, higher than 34.9% of scored vulnerabilities.
CVSS score
9.1/10
010
Critical · v3.1 (CVE.org)EPSS score
0.42%
0%100%
Low · +0.18 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Advisory lineage
Upstream 0 · Downstream 1 · Related 1Timeline
- 01-04-2026PublishedVulnerability first disclosed.
- 02-04-2026Last modifiedVulnerability information updated.
Description
An issue was discovered in Mbed TLS 3.5.0 through 4.0.0. Client impersonation can occur while resuming a TLS 1.3 session.
CVSS metrics
4 scores · 4 sources · 1 versionCritical 9.1Preferred score · CVE.org (CNA)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:NSourcesAll 4 agree
- OSV · UbuntuEcosystem advisory · calculated9.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- OSV · DebianEcosystem advisory · calculated9.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- NVDNIST9.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
EPSS trend
Probability
0.42%
Chance of exploitation in the next 30 days
Percentile
35%
Versus all other CVEs
30-day change
+0.18 pp
From 0.24% on 20-09-2026
20-09-202620-10-2026
EPSS score0.42%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Debian1 product
- mbedtlsAll versions (No fix recorded) | < 3.6.6-0.1~deb13u1 | < 3.6.6-0.1
Trustedfirmware1 product
- mbed_tls≥ 3.5.0, < 3.6.6 | ≥ 4.0.0, < 4.1.0
Ubuntu1 product
- mbedtlsAll versions (No fix recorded)
3 vendors · 3 products
