VulnerabilityPublished 21 Jan 2024Updated 30 May 2025

CVE-2023-52353: Mbed TLS · Session Fixation

Source CVE Database V5

Not known to be exploited · CVSS 7.5 High.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 0.4% chance of exploitation in 30 days – higher than 39% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

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

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: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
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: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 21 Jan 2024
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

Affected software

Product	Affected	Fixed in
GitHubmbed-tls/mbedtls`pkg:github/mbed-tls/mbedtls`Other threats	Affected <=3.5.1	Fixed in–

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

AI-suggested

Organizations should first identify all systems and devices using Mbed TLS up to version 3.5.1. Until an official patch is released, mitigating this vulnerability involves: 1) Implementing strict TLS version enforcement policies at the application or network level to prevent fallback to older TLS versions; 2) Using network security controls such as TLS interception proxies or firewalls capable of enforcing minimum TLS versions; 3) Monitoring TLS negotiation logs for unexpected downgrades or anomalies; 4) Coordinating with device and software vendors to obtain updates or patches as soon as they become available; 5) For embedded devices, consider firmware updates or replacements if patching is not feasible; 6) Employing additional layers of encryption or integrity checks at the application layer to mitigate risks from TLS downgrade; 7) Conducting regular security assessments and penetration testing focused on TLS configurations and cryptographic implementations.

Description

An issue was discovered in Mbed TLS through 3.5.1. In mbedtls_ssl_session_reset, the maximum negotiable TLS version is mishandled. For example, if the last connection negotiated TLS 1.2, then 1.2 becomes the new maximum.

Impact

For European organizations, this vulnerability poses a risk to the security of encrypted communications that rely on Mbed TLS, a widely used open-source cryptographic library in embedded systems, IoT devices, and network appliances. Downgrading the TLS version to 1.2 or lower can expose sensitive data to interception or manipulation due to weaker cipher suites and known vulnerabilities in older TLS versions. This is particularly critical for sectors handling sensitive personal data under GDPR, such as finance, healthcare, and government services. The integrity of secure communications could be compromised, potentially leading to data breaches or man-in-the-middle attacks. Moreover, the forced downgrade could undermine trust in secure channels, affecting compliance with European cybersecurity regulations and standards. Since Mbed TLS is often embedded in devices with limited update capabilities, the risk of prolonged exposure is higher, especially in critical infrastructure and industrial control systems prevalent in Europe.

CWE-384Session Fixation (opens in a new tab)
Compound weaknessOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
Authenticating a user, or otherwise establishing a new user session, without invalidating any existing session identifier gives an attacker the opportunity to steal authenticated sessions.
Architecture and Design
Invalidate any existing session identifiers prior to authorizing a new user session.
Architecture and Design
For platforms such as ASP that do not generate new values for sessionid cookies, utilize a secondary cookie. In this approach, set a secondary cookie on the user's browser to a random value and set a session variable to the same value.
Operation · Firewall
Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.
OWASP Cheat Sheets
Session Management (opens in a new tab)
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V3.2.1 (opens in a new tab)
Attack patterns
Session Credential Falsification through Forging (opens in a new tab)
Accessing/Intercepting/Modifying HTTP Cookies (opens in a new tab)
Manipulating Opaque Client-based Data Tokens (opens in a new tab)
Session Credential Falsification through Prediction (opens in a new tab)
Reusing Session IDs (aka Session Replay) (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/Mbed-TLS/mbedtls/issues/8654 (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 8 Jul 2025, 16:28 UTC

WeaknessesCWE-384

Technical details

References

Community reviews

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