CVE-2021-45450
Description
In Mbed TLS before 2.28.0 and 3.x before 3.1.0, PSA cipher APIs can bypass policy or enable oracle-based decryption when the output buffer is in untrusted memory.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
In Mbed TLS before 2.28.0 and 3.x before 3.1.0, PSA cipher APIs can bypass policy or enable oracle-based decryption when the output buffer is in untrusted memory.
Vulnerability
In Mbed TLS versions before 2.28.0 and 3.x before 3.1.0, the PSA Crypto APIs psa_cipher_generate_iv and psa_cipher_encrypt allow a policy bypass or oracle-based decryption when the output buffer is located at memory accessible to an untrusted application [1][2]. The issue arises because these functions do not properly restrict access to the output buffer, potentially allowing disclosure of sensitive data or algorithm parameters.
Exploitation
An attacker must have the ability to control or observe memory locations where the output buffer of these PSA cipher functions resides. This typically requires local access to the system where Mbed TLS is running, and the attacker's application must be able to read the output buffer after the function completes. The attacker does not need authentication to the targeted TLS server or client; they merely need to be in a position to influence the buffer location (e.g., via shared memory or pre‑allocated regions). The exploitation steps involve: (1) arranging for the output buffer to be in a memory region readable by the attacker, (2) triggering the vulnerable psa_cipher_generate_iv or psa_cipher_encrypt call, and (3) reading the output to obtain the generated IV or ciphertext, which can then be used to deduce encryption keys or bypass security policies.
Impact
Successful exploitation can lead to policy bypass, where an attacker can encrypt data without proper authorization, or enable an oracle‑based decryption attack by observing the generated IV or ciphertext output. This compromises the confidentiality of encrypted communications and undermines the security guarantees provided by the PSA Crypto API. The attacker does not escalate privileges but can read sensitive cryptographic material, potentially enabling further attacks on encrypted data.
Mitigation
Mbed TLS 2.28.0 (LTS branch) and 3.1.0 (current branch) contain the fix for this vulnerability [1][2]. Users should upgrade to these versions or later. No workarounds are documented. The vulnerability was published on 2021‑12‑21 and patches are available in the referenced releases.
AI Insight generated on May 27, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected products
3- Mbed TLS/Mbed TLSdescription
Patches
0No patches discovered yet.
Vulnerability mechanics
Root cause
"psa_cipher_generate_iv and psa_cipher_encrypt read back from the output buffer after writing to it, allowing a policy bypass or decryption oracle when the buffer is in memory shared with an untrusted application."
Attack vector
An attacker who can share memory with a victim application (e.g., through shared memory or a sandbox escape) can exploit the fact that `psa_cipher_generate_iv()` and `psa_cipher_encrypt()` read back from the output buffer after writing to it. By modifying the output buffer between the write and the read, the attacker can cause the functions to use attacker-controlled data as the IV or ciphertext, leading to a policy bypass or enabling a decryption oracle attack. No network path or authentication is required beyond the ability to access the same memory region.
Affected code
The vulnerability resides in `psa_cipher_generate_iv()` and `psa_cipher_encrypt()` in Mbed TLS before 2.28.0 and 3.x before 3.1.0. These functions read back from the output buffer after writing to it, which is the root cause of the issue.
What the fix does
The patch removes the read-back from the output buffer in `psa_cipher_generate_iv()` and `psa_cipher_encrypt()`. Previously, these functions wrote the IV or ciphertext into the output buffer and then read the same buffer back for subsequent operations. If the output buffer resided in memory shared with an untrusted application, the untrusted application could alter the buffer contents between the write and the read, causing the library to use attacker-controlled data. By eliminating the read-back, the fix ensures that the library uses only the internally computed values, closing the policy bypass and decryption oracle attack surface.
Preconditions
- configThe output buffer passed to psa_cipher_generate_iv() or psa_cipher_encrypt() must be located in memory that is accessible to an untrusted application (e.g., shared memory).
- inputThe attacker must be able to write to that shared memory region concurrently with the victim's use of the affected functions.
Generated on May 30, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
5- github.com/ARMmbed/mbedtls/releases/tag/v2.28.0nvdRelease NotesThird Party Advisory
- github.com/ARMmbed/mbedtls/releases/tag/v3.1.0nvdRelease NotesThird Party Advisory
- security.gentoo.org/glsa/202301-08nvdThird Party Advisory
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IL66WKJGXY5AXMTFE7QDMGL3RIBD6PX5/nvdMailing List
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TALJHOYAYSUJTLN6BYGLO4YJGNZUY74W/nvdMailing List
News mentions
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