CVE-2026-33753Public exploit

TSA impersonation via naïve leaf certificate selection

Published Apr 8, 2026 · Updated Apr 8, 2026

Improper certificate validation in Trail of Bits rfc3161-client before 1.0.6 allows attackers to impersonate a trusted TSA. Verifier._verify_leaf_certs selects the first non-issuer certificate from an unordered PKCS#7 bag, then checks TSA pinning against that certificate instead of the signed SignerInfo identity. Attackers able to modify a timestamp response can inject qualifying certificates, causing an authentic timestamp from any trusted TSA to be accepted under a pinned TSA identity.

CVSS severity6.2
Medium
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in Trail of Bits rfc3161-client before 1.0.6 allows attackers to impersonate a trusted TSA. Verifier._verify_leaf_certs selects the first non-issuer certificate from an unordered PKCS#7 bag, then checks TSA pinning against that certificate instead of the signed SignerInfo identity. Attackers able to modify a timestamp response can inject qualifying certificates, causing an authentic timestamp from any trusted TSA to be accepted under a pinned TSA identity.

The record

CVE
CVE-2026-33753
Published
Apr 8, 2026
Updated
Apr 8, 2026
Vendor
Trail of Bits
Product
rfc3161-client
Classifications
CWE-295, T1553
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 8, 2026Record 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=< 1.0.6

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Trail of Bits · rfc3161-clientversion=< 1.0.6

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
6.2GitHub, Inc.CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-295Improper Certificate Validation
T1553Subvert Trust Controls

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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