VulnerabilityPublished 3 Nov 2025

CVE-2024-27306: aio-libs aiohttp · Cross-site Scripting

Affects aio-libs aiohttpSource CVE Database V5

Not known to be exploited · CVSS 6.1 Medium : upgrade to 3.9.4 when convenient.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 3.1 base score

6.1Medium

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

EPSS: 0.6% chance of exploitation in 30 days – higher than 51% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.9.4

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Changed
Confidentiality: Low
Integrity: Low
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: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
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: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to 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: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 3 Nov 2025
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 aio-libs aiohttp to 3.9.4.

Affected software

Product	Affected	Fixed in
PyPIaiohttp`pkg:pypi/aiohttp`Other threats	Affected <3.9.4	Fixed in 3.9.4

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

AI-suggested

Upgrade aiohttp to version 3.9.4 or later immediately to apply the official fix for CVE-2024-27306.
If upgrading is not feasible in the short term, disable the 'show_index' feature in aiohttp configurations to prevent directory index pages from being generated.
Deploy a reverse proxy server such as nginx or Apache to serve static files, isolating static content delivery from aiohttp and mitigating the vulnerability.
Conduct a thorough audit of aiohttp usage across all web services to identify instances where static file serving with directory indexes is enabled.
Implement Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers, reducing the impact of potential XSS attacks.
Educate developers and system administrators about secure configuration practices for aiohttp and the risks of enabling directory indexes.
Monitor web server logs for suspicious requests targeting static file directories and unusual query parameters that could indicate attempted exploitation.
Integrate vulnerability scanning and automated patch management to ensure timely updates of aiohttp and dependent components.

Description

### Summary A XSS vulnerability exists on index pages for static file handling. ### Details When using `web.static(..., show_index=True)`, the resulting index pages do not escape file names. If users can upload files with arbitrary filenames to the static directory, the server is vulnerable to XSS attacks. ### Workaround We have always recommended using a reverse proxy server (e.g. nginx) for serving static files. Users following the recommendation are unaffected. Other users can disable `show_index` if unable to upgrade. ----- Patch: https://github.com/aio-libs/aiohttp/pull/8319/files

Impact

For European organizations, the impact of this vulnerability can be significant in environments where aiohttp is used to serve web applications or APIs that include static file hosting with directory indexes enabled. Successful exploitation could lead to the compromise of user sessions, leakage of sensitive data, and unauthorized actions performed under the victim's identity, undermining confidentiality and integrity. While availability is not directly affected, the reputational damage and potential regulatory consequences under GDPR for data breaches could be substantial. Organizations relying on aiohttp without a reverse proxy or with 'show_index' enabled are at higher risk. The threat is particularly relevant for sectors with high web service usage such as finance, healthcare, and public services, where sensitive data is processed. The lack of known exploits in the wild suggests a window of opportunity for proactive mitigation before attackers develop weaponized payloads.

Summary

CVE-2024-27306 is a Cross-site Scripting (XSS) vulnerability identified in aiohttp, an asynchronous HTTP client/server framework widely used in Python applications. The vulnerability exists in the index pages generated for static file handling when the 'show_index' feature is enabled. Specifically, the flaw stems from improper neutralization of user input during web page generation, classified under CWE-79 and CWE-80, which allows malicious actors to inject and execute arbitrary JavaScript code in the context of users' browsers. This can lead to theft of session tokens, user credentials, or other sensitive information, as well as unauthorized actions performed on behalf of the user. The vulnerability affects aiohttp versions prior to 3.9.4 and does not require authentication but does require user interaction, such as visiting a crafted URL. The developers recommend using a reverse proxy server like nginx to serve static files, which effectively mitigates the risk by isolating static content delivery from aiohttp's vulnerable index page generation. For users unable to upgrade immediately, disabling the 'show_index' feature is advised to prevent exposure. No known exploits are currently reported in the wild, but the medium CVSS score of 6.1 reflects the potential impact and ease of exploitation. The vulnerability's scope is limited to aiohttp deployments that serve static files with directory indexes enabled, which is common in development and some production environments.

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #1OWASP Top 10 A05:2025: Injection (opens in a new tab)
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Implementation · Architecture and Design
Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages.
Architecture and Design · Implementation · Attack Surface Reduction
Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide…
OWASP Cheat Sheets
Cross Site Scripting Prevention (opens in a new tab)
DOM based XSS Prevention (opens in a new tab)
Injection Prevention (opens in a new tab)
Abuse Case (opens in a new tab)
Deserialization (opens in a new tab)
OWASP ASVS 4.0.3
V5.3.3 (opens in a new tab)
V1.5.1 (opens in a new tab)
Attack patterns
XSS Using MIME Type Mismatch (opens in a new tab)
DOM-Based XSS (opens in a new tab)
Reflected XSS (opens in a new tab)
Stored XSS (opens in a new tab)
Cross-Site Scripting (XSS) (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-80Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS) (opens in a new tab)
Variant weaknessLikelihood of exploit: HighOWASP Top 10 A05:2025: Injection (opens in a new tab)
The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as "<", ">", and "&" that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages.
Implementation
Carefully check each input parameter against a rigorous positive specification (allowlist) defining the specific characters and format allowed. All input should be neutralized, not just parameters that the user is supposed to specify, but all data in the request, including hidden fields, cookies, headers, the URL…
Implementation · Output Encoding
Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8.
Implementation
With Struts, write all data from form beans with the bean's filter attribute set to true.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
Deserialization (opens in a new tab)
Cross Site Scripting Prevention (opens in a new tab)
DOM based XSS Prevention (opens in a new tab)
Injection Prevention (opens in a new tab)
OWASP ASVS 4.0.3
V1.5.1 (opens in a new tab)
V5.3.3 (opens in a new tab)
Attack patterns
XSS Targeting Non-Script Elements (opens in a new tab)
PHP Remote File Inclusion (opens in a new tab)
XSS Through HTTP Query Strings (opens in a new tab)
XSS Through HTTP Headers (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 3 Nov 2025, 22:11 UTC

WeaknessesCWE-79, CWE-80

Technical details

References

Community reviews

Related threats