VulnerabilityPublished 7 Feb 2023Updated 3 Nov 2025

CVE-2023-23931: pyca cryptography · Unchecked Error Condition

Affects pyca cryptographySource CVE Database V5

Not known to be exploited · CVSS 4.8 Medium : upgrade to 1.8 when convenient.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score

4.8Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 1.3% chance of exploitation in 30 days – higher than 70% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.8

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 7 Feb 2023
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade pyca cryptography to 1.8.

Affected software

Product	Affected	Fixed in
PyPIcryptography`pkg:pypi/cryptography`Other threats	Affected <1.8	Fixed in 1.8

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

The most effective mitigation is to upgrade the pyca cryptography package to version 39.0.1 or later, where the vulnerability is fixed by raising exceptions when immutable buffers are passed to Cipher.update_into. Organizations should audit their Python environments and dependencies to identify usage of vulnerable versions (>=1.8, <39.0.1) and apply updates promptly. For environments where immediate upgrade is not feasible, developers should review code paths invoking update_into to ensure only mutable buffer objects are passed, avoiding immutable types like bytes. Implementing rigorous input validation and buffer type checks before cryptographic operations can reduce risk. Additionally, incorporating integrity checks and monitoring cryptographic outputs for anomalies can help detect potential exploitation or corruption. Security teams should also verify that their software supply chain and CI/CD pipelines enforce dependency version controls to prevent reintroduction of vulnerable versions. Finally, maintaining awareness of pyca cryptography releases and security advisories will support timely response to future vulnerabilities.

Description

cryptography is a package designed to expose cryptographic primitives and recipes to Python developers. In affected versions `Cipher.update_into` would accept Python objects which implement the buffer protocol, but provide only immutable buffers. This would allow immutable objects (such as `bytes`) to be mutated, thus violating fundamental rules of Python and resulting in corrupted output. This now correctly raises an exception. This issue has been present since `update_into` was originally introduced in cryptography 1.8.

Impact

For European organizations, the primary impact of CVE-2023-23931 lies in the potential corruption of cryptographic operations that rely on the pyca cryptography package. This can affect applications performing encryption, decryption, or message authentication, potentially leading to data integrity issues or application failures. While confidentiality is not directly compromised, corrupted cryptographic outputs can cause denial of service or incorrect processing of secure communications. Organizations in sectors such as finance, healthcare, government, and critical infrastructure that depend on Python-based cryptographic libraries for secure data handling are at risk of operational disruptions. The vulnerability could undermine trust in cryptographic processes, complicate compliance with data protection regulations like GDPR, and increase the risk of cascading failures in security-sensitive systems. Since exploitation requires no authentication or user interaction but has high complexity, the risk of widespread automated attacks is limited but non-negligible. European entities using outdated versions of pyca cryptography should assess their exposure and prioritize remediation to maintain cryptographic integrity.

CWE-754Improper Check for Unusual or Exceptional Conditions (opens in a new tab)
Class weaknessLikelihood of exploit: MediumOWASP Top 10 A10:2025: Mishandling of Exceptional Conditions (opens in a new tab)
The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.
Requirements · Language Selection
Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Implementation
Check the results of all functions that return a value and verify that the value is expected.
Implementation
If using exception handling, catch and throw specific exceptions instead of overly-general exceptions (CWE-396, CWE-397). Catch and handle exceptions as locally as possible so that exceptions do not propagate too far up the call stack (CWE-705). Avoid unchecked or uncaught exceptions where feasible (CWE-248).
OWASP Cheat Sheets
Logging (opens in a new tab)
Error Handling (opens in a new tab)
OWASP ASVS 4.0.3
V11.1.7 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 4 Nov 2025, 00:10 UTC

WeaknessesCWE-754

Technical details

References

Community reviews

Related threats