CVE-2023-43630: PCR14 mismeasurement in TPM2 sealed vault
CVE-2023-43630 Published on September 20, 2023
Config Partition Not Measured From 2 Fronts
PCR14 is not in the list of PCRs that seal/unseal the vault key, but
due to the change that was implemented in commit
7638364bc0acf8b5c481b5ce5fea11ad44ad7fd4, fixing this issue alone would not solve the
problem of the config partition not being measured correctly.
Also, the vault key is sealed/unsealed with SHA1 PCRs instead of
SHA256.
This issue was somewhat mitigated due to all of the PCR extend functions
updating both the values of SHA256 and SHA1 for a given PCR ID.
However, due to the change that was implemented in commit
7638364bc0acf8b5c481b5ce5fea11ad44ad7fd4, this is no longer the case for PCR14, as
the code in measurefs.go explicitly updates only the SHA256 instance of PCR14, which
means that even if PCR14 were to be added to the list of PCRs sealing/unsealing the vault
key, changes to the config partition would still not be measured.
An attacker could modify the config partition without triggering the measured boot, this could
result in the attacker gaining full control over the device with full access to the contents of the
encrypted vault
Vulnerability Analysis
CVE-2023-43630 is exploitable with local system access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Types
Insufficiently Protected Credentials
The product transmits or stores authentication credentials, but it uses an insecure method that is susceptible to unauthorized interception and/or retrieval.
Insecure Storage of Sensitive Information
The software stores sensitive information without properly limiting read or write access by unauthorized actors. If read access is not properly restricted, then attackers can steal the sensitive information. If write access is not properly restricted, then attackers can modify and possibly delete the data, causing incorrect results and possibly a denial of service.
Reversible One-Way Hash
The product uses a hashing algorithm that produces a hash value that can be used to determine the original input, or to find an input that can produce the same hash, more efficiently than brute force techniques. This weakness is especially dangerous when the hash is used in security algorithms that require the one-way property to hold. For example, if an authentication system takes an incoming password and generates a hash, then compares the hash to another hash that it has stored in its authentication database, then the ability to create a collision could allow an attacker to provide an alternate password that produces the same target hash, bypassing authentication.
Products Associated with CVE-2023-43630
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Affected Versions
LF-Edge, Zededa EVE OS:- Version 9.0.0 and below 9.5.0 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.