CVE-2026-31790

Incorrect Failure Handling in RSA KEM RSASVE Encapsulation

Published Apr 7, 2026 CVSS 3.1 · 7.5 High EPSS 1.0% KEV · Not listed
Description
Issue summary: Applications using RSASVE key encapsulation to establish
a secret encryption key can send contents of an uninitialized memory buffer to
a malicious peer.

Impact summary: The uninitialized buffer might contain sensitive data from the
previous execution of the application process which leads to sensitive data
leakage to an attacker.

RSA_public_encrypt() returns the number of bytes written on success and -1
on error. The affected code tests only whether the return value is non-zero.
As a result, if RSA encryption fails, encapsulation can still return success to
the caller, set the output lengths, and leave the caller to use the contents of
the ciphertext buffer as if a valid KEM ciphertext had been produced.

If applications use EVP_PKEY_encapsulate() with RSA/RSASVE on an
attacker-supplied invalid RSA public key without first validating that key,
then this may cause stale or uninitialized contents of the caller-provided
ciphertext buffer to be disclosed to the attacker in place of the KEM
ciphertext.

As a workaround calling EVP_PKEY_public_check() or
EVP_PKEY_public_check_quick() before EVP_PKEY_encapsulate() will mitigate
the issue.

The FIPS modules in 3.6, 3.5, 3.4, 3.3, 3.1 and 3.0 are affected by this issue.

Analysis

AI-generated

Technical impact

Applications using RSA/RSASVE key encapsulation can mistakenly treat a failure of RSA_public_encrypt as a success because the code only checks for a non‑zero return value. When encryption fails, the function still returns a length and the caller believes a valid KEM ciphertext was produced, causing stale or uninitialized ciphertext data to be sent to a peer. The contents of that buffer may contain previously used memory and can reveal secrets or other sensitive information. This flaw is a case of improper failure handling (CWE‑754) and insecure data exposure (CWE‑824).

Affected Systems

The OpenSSL library and all FIPS modules in versions 3.0 through 3.6 are affected. Any application that links against these releases and performs RSA/RSASVE encapsulation without validating the RSA public key may be vulnerable.

Risk and Exploitability

The CVSS score of 7.5 indicates medium‑to‑high severity and the EPSS score of less than 1% suggests a low current exploitation probability; it is not listed in CISA’s KEV catalog. Based on the description, it is inferred that an attacker can trigger the failure path by submitting an invalid RSA public key to the vulnerable application. If the application exposes a network or interprocess interface that accepts such keys, the attack may be remote; otherwise, local or privileged access might be required. The exploitation results in memory contents leaking from the victim’s address space, potentially revealing private keys, configuration data, or other sensitive items, but the risk level depends heavily on how the application validates keys and handles errors.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Apply the OpenSSL patch that resolves CVE‑2026‑31790
  • If patching is not possible, validate RSA keys before encapsulation by calling EVP_PKEY_public_check or EVP_PKEY_public_check_quick

Generated by OpenCVE AI on April 8, 2026 at 17:23 UTC.

Tracking

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Advisories

Source ID Title
Debian DSA Debian DSA DSA-6201-1 openssl security update
Ubuntu USN Ubuntu USN USN-8155-1 OpenSSL vulnerabilities
History
Type Values Removed Values Added
CPEs cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
Type Values Removed Values Added
First Time appeared Openssl
Openssl openssl
Vendors & Products Openssl
Openssl openssl
Type Values Removed Values Added
Metrics cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N'}

Type Values Removed Values Added
Weaknesses CWE-824
References
Metrics threat_severity

None

cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N'}

threat_severity

Moderate

Type Values Removed Values Added
Description Issue summary: Applications using RSASVE key encapsulation to establish a secret encryption key can send contents of an uninitialized memory buffer to a malicious peer. Impact summary: The uninitialized buffer might contain sensitive data from the previous execution of the application process which leads to sensitive data leakage to an attacker. RSA_public_encrypt() returns the number of bytes written on success and -1 on error. The affected code tests only whether the return value is non-zero. As a result, if RSA encryption fails, encapsulation can still return success to the caller, set the output lengths, and leave the caller to use the contents of the ciphertext buffer as if a valid KEM ciphertext had been produced. If applications use EVP_PKEY_encapsulate() with RSA/RSASVE on an attacker-supplied invalid RSA public key without first validating that key, then this may cause stale or uninitialized contents of the caller-provided ciphertext buffer to be disclosed to the attacker in place of the KEM ciphertext. As a workaround calling EVP_PKEY_public_check() or EVP_PKEY_public_check_quick() before EVP_PKEY_encapsulate() will mitigate the issue. The FIPS modules in 3.6, 3.5, 3.4, 3.3, 3.1 and 3.0 are affected by this issue.
Title Incorrect Failure Handling in RSA KEM RSASVE Encapsulation
Weaknesses CWE-754
References
Weaknesses
  • CWE-754

    Improper Check for Unusual or Exceptional Conditions

  • CWE-824

    Access of Uninitialized Pointer

Sources

Status
PUBLISHED
Assigner
openssl
Published
Updated
May 12, 2026, 12:09 PM
Reserved
Mar 9, 2026, 3:56 PM
Status
Modified
Published
Apr 7, 2026, 10:16 PM
Modified
Jul 24, 2026, 11:10 PM
Severity
Moderate
Public date
Apr 7, 2026, 12:00 AM