CVE-2020-13777Network attack vector

Authentication bypass via uninitialized session-ticket key

Published Jun 4, 2020 · Updated Aug 4, 2024

Cryptographic flaw in GnuTLS 3.6.4 through 3.6.13 allows man-in-the-middle attackers to bypass TLS 1.3 authentication via session resumption. In lib/stek.c, initial session-ticket setup records the TOTP timestamp without initializing the application-supplied key, so tickets use wrong key data until rotation. An active network interception position is required; successful attacks bypass TLS 1.3 authentication or recover earlier TLS 1.2 conversations.

CVSS severity7.4
High
EPSS probability17.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cryptographic flaw in GnuTLS 3.6.4 through 3.6.13 allows man-in-the-middle attackers to bypass TLS 1.3 authentication via session resumption. In lib/stek.c, initial session-ticket setup records the TOTP timestamp without initializing the application-supplied key, so tickets use wrong key data until rotation. An active network interception position is required; successful attacks bypass TLS 1.3 authentication or recover earlier TLS 1.2 conversations.

The record

CVE
CVE-2020-13777
Published
Jun 4, 2020
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-327, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 4, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:N
7.4NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-327Use of a Broken or Risky Cryptographic Algorithm
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

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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