CyberSecBulletin
CVE-2023-45287NVD status: Modified

crypto/tls: Observable Discrepancy

Published Updated By the CyberSecBulletin desk

CVE-2023-45287 is a high-severity observable discrepancy vulnerability in crypto/tls from Go standard library, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 1.20.0 as the first without the flaw, so updating crypto/tls to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 1.25% chance of exploitation within 30 days, higher than 70% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update crypto/tls to 1.20.0 or a later version.
  2. Update Go to 1.20.0 or a later version.
  3. Read the advisory on pkg.go.dev for workarounds and exact fixed builds.
  4. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
Go standard librarycrypto/tlsbefore 1.20.01.20.0
GoGobefore 1.20.01.20.0

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
NoneNothing can be modified.
Availability
NoneAvailability is not affected.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. Scored by NVD.

Official description

Before Go 1.20, the RSA based TLS key exchanges used the math/big library, which is not constant time. RSA blinding was applied to prevent timing attacks, but analysis shows this may not have been fully effective. In particular it appears as if the removal of PKCS#1 padding may leak timing information, which in turn could be used to recover session key bits. In Go 1.20, the crypto/tls library switched to a fully constant time RSA implementation, which we do not believe exhibits any timing side channels.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Observable Discrepancy

The product behaves differently or sends different responses under different circumstances in a way that is observable to an unauthorized actor.

How developers prevent this class of flaw

  • Compartmentalize the system to have safe areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

More Observable Discrepancy vulnerabilities (CWE-203)

Timeline

  1. CVE record published.
  2. Record last changed materially (score, affected products, status or references).

References

Patches and release notes

Third-party and government advisories

Other vulnerabilities in crypto/tls

All crypto/tls vulnerabilities

Recent Observable Discrepancy vulnerabilities

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