VulnerabilityPublished 20 Mar 2026

CVE-2026-33054: mesop · Path Traversal

Affects mesopSource CVE Database V5

Compare

Not known to be exploited · CVSS 10.0 Critical : upgrade to 1.2.3 as a priority.

Data as of 31 Oct 2026, 20:20 UTC

CVSS 3.1 base score

10.0Critical

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

EPSS: 0.7% chance of exploitation in 30 days – higher than 54% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.2.3

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

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

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: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
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: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 20 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 31 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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 mesop to 1.2.3.

Affected software

Product	Affected	Fixed in
mesop-devmesop	Affected <1.2.3	Fixed in 1.2.3
PyPImesop`pkg:pypi/mesop`Other threats	Affected <1.2.3	Fixed in 1.2.3

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

AI-suggested

To mitigate CVE-2026-33054, organizations should immediately upgrade mesop to version 1.2.3 or later, where the vulnerability is patched. Until upgrading is possible, disable or avoid using the FileStateSessionBackend to prevent exposure to the path traversal flaw. Implement strict input validation and sanitization on all user-supplied parameters, especially state_token inputs, to block directory traversal sequences such as '../'. Employ runtime application self-protection (RASP) or web application firewalls (WAFs) configured to detect and block path traversal attempts targeting mesop endpoints. Conduct thorough code reviews and penetration testing focusing on file handling logic within the application. Additionally, restrict file system permissions for the application process to the minimum necessary, preventing unauthorized file modifications outside designated directories. Monitor logs for suspicious file access patterns and anomalous crashes indicative of exploitation attempts.

Description

Mesop is a Python-based UI framework that allows users to build web applications. Versions 1.2.2 and below contain a Path Traversal vulnerability that allows any user supplying an untrusted state_token through the UI stream payload to arbitrarily target files on the disk under the standard file-based runtime backend. This can result in application denial of service (via crash loops when reading non-msgpack target files as configurations), or arbitrary file manipulation. This vulnerability heavily exposes systems hosted utilizing FileStateSessionBackend. Unauthorized malicious actors could interact with arbitrary payloads overwriting or explicitly removing underlying service resources natively outside the application bounds. This issue has been fixed in version 1.2.3.

Impact

The impact of CVE-2026-33054 is severe and multifaceted. Organizations running vulnerable versions of mesop with the FileStateSessionBackend are at risk of remote, unauthenticated attackers gaining arbitrary file read/write capabilities on the host system. This can lead to unauthorized disclosure of sensitive data, modification or deletion of critical application or system files, and complete denial of service due to application crashes. In worst-case scenarios, attackers could leverage this access to escalate privileges or establish persistent footholds, severely compromising the confidentiality, integrity, and availability of affected systems. Given mesop’s role in web application UI frameworks, exploitation could disrupt business-critical web services, damage reputation, and cause significant operational downtime. The vulnerability’s ease of exploitation and lack of required authentication make it a high-risk threat globally.

Summary

Mesop is a Python-based UI framework designed for building web applications, which in versions 1.2.2 and earlier contains a severe path traversal vulnerability (CWE-22) identified as CVE-2026-33054. This vulnerability arises from improper limitation of pathname inputs in the FileStateSessionBackend, where an attacker can supply an untrusted state_token parameter through the UI stream payload. Because the backend relies on file-based runtime sessions, the crafted input allows an attacker to traverse directories arbitrarily and access or manipulate files on the host filesystem. This can cause application denial of service by forcing the application into crash loops when it attempts to read non-msgpack files as configuration data. More critically, attackers can overwrite or delete essential service files outside the application’s intended boundaries, potentially leading to full compromise of the host system. The vulnerability requires no authentication or user interaction and can be exploited remotely over the network. The issue was addressed and fixed in mesop version 1.2.3. The CVSS v3.1 base score is 10.0, reflecting critical impact on confidentiality, integrity, and availability, with low attack complexity and no privileges required.

CWE-22Improper Limitation of a Pathname to a Restricted Directory (Path Traversal) (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #6OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
Architecture and Design
For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks…
Implementation · Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174).
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V12.3.1 (opens in a new tab)
Attack patterns
Path Traversal (opens in a new tab)
Using Slashes and URL Encoding Combined to Bypass Validation Logic (opens in a new tab)
Manipulating Web Input to File System Calls (opens in a new tab)
Using Escaped Slashes in Alternate Encoding (opens in a new tab)
Using Slashes in Alternate Encoding (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 20 Mar 2026, 07:38 UTC

WeaknessesCWE-22

Technical details

References

Community reviews

Related threats