VulnerabilityPublished 14 Nov 2023Updated 3 Nov 2025

CVE-2023-47627: aio-libs aiohttp · HTTP Request/Response Smuggling

Affects aio-libs aiohttpSource CVE Database V5

Not known to be exploited · CVSS 5.3 Medium : upgrade to 3.8.6 when convenient.

Data as of 26 Oct 2026, 15:59 UTC

CVSS 3.1 base score

5.3Medium

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

EPSS: 0.8% chance of exploitation in 30 days – higher than 58% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.8.6

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
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: 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: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 14 Nov 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 aio-libs aiohttp to 3.8.6.

Affected software

Product	Affected	Fixed in
PyPIaiohttp`pkg:pypi/aiohttp`Other threats	Affected <3.8.6	Fixed in 3.8.6

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

AI-suggested

The primary mitigation is to upgrade all aiohttp installations to version 3.8.6 or later, where the vulnerability has been fixed. Organizations should audit their Python environments to identify any use of aiohttp, especially in configurations where AIOHTTP_NO_EXTENSIONS is set or where prebuilt wheels are not used. If upgrading immediately is not feasible, consider enforcing the use of prebuilt wheels or enabling extensions to avoid the vulnerable parser. Network-level protections such as strict HTTP header validation and deploying web application firewalls with rules to detect request smuggling attempts can provide additional defense layers. Monitoring HTTP traffic for anomalies and unusual request patterns may help detect exploitation attempts. Developers should review their HTTP handling code for reliance on vulnerable aiohttp versions and avoid custom builds that disable extensions unless necessary. Finally, maintain awareness of updates from aio-libs and apply security patches promptly.

Description

aiohttp is an asynchronous HTTP client/server framework for asyncio and Python. The HTTP parser in AIOHTTP has numerous problems with header parsing, which could lead to request smuggling. This parser is only used when AIOHTTP_NO_EXTENSIONS is enabled (or not using a prebuilt wheel). These bugs have been addressed in commit `d5c12ba89` which has been included in release version 3.8.6. Users are advised to upgrade. There are no known workarounds for these issues.

Impact

For European organizations, the impact of CVE-2023-47627 depends largely on their use of aiohttp in configurations that disable extensions or use custom builds without prebuilt wheels. Organizations running asynchronous Python web services or APIs that rely on aiohttp could face risks of HTTP request smuggling attacks, which may lead to bypassing security controls such as web application firewalls, session hijacking, or cache poisoning. This can compromise the integrity of web applications and potentially expose internal services or sensitive data indirectly. Given the widespread adoption of Python and asyncio frameworks in European tech sectors, especially in fintech, e-commerce, and public sector digital services, the vulnerability could be leveraged to disrupt services or facilitate further attacks. However, the lack of known active exploitation and the medium severity rating suggest the immediate risk is moderate but should not be underestimated. Failure to patch could lead to increased exposure to sophisticated attackers targeting web infrastructure.

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') (opens in a new tab)
Base weaknessOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
Implementation
Use a web server that employs a strict HTTP parsing procedure, such as Apache.
Implementation
Use only SSL communication.
Implementation
Terminate the client session after each request.
OWASP Cheat Sheets
REST Assessment (opens in a new tab)
REST Security (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V13.2.5 (opens in a new tab)
Attack patterns
HTTP Response Smuggling (opens in a new tab)
HTTP Request Smuggling (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 3 Nov 2025, 22:06 UTC

WeaknessesCWE-444

Technical details

References

Community reviews

Related threats