aiohttp: Improper Validation of Certificate with Host Mismatch
CVE-2026-54275 is a high-severity improper validation of certificate with host mismatch vulnerability in aiohttp from Aio-libs, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected aiohttp versions: < 3.14.1. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.47% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of aiohttp you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 2.7 | Low | CNA (github.com) |
| CVSS 3.1 | 7.5 | High | NVD |
Official description
AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.1, the server_hostname TLS SNI check can be bypassed when an existing connection is reused. If an application makes multiple requests to the same domain, but with different per-request server_hostname parameters, then the later calls may succeed by reusing the existing connection when they should have been rejected due to the TLS SNI check. This vulnerability is fixed in 3.14.1.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Validation of Certificate with Host Mismatch
The product communicates with a host that provides a certificate, but the product does not properly ensure that the certificate is actually associated with that host.
How developers prevent this class of flaw
- In order to ensure data integrity, the certificate must be valid, and it must pertain to the site that is being accessed.Fully check the hostname of the certificate and provide the user with adequate information about the nature of the problem and how to proceed.
- If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.
- Be careful of other weaknesses in the code that checks the hostname, since it is still possible to incorrectly check the hostname. For example, attackers could create a certificate with a name that begins with a trusted name followed by a NUL byte, which could cause some string-based comparisons to only examine the portion that contains the trusted name.
More Improper Validation of Certificate with Host Mismatch vulnerabilities (CWE-297)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- github.com/aio-libs/aiohttp/security/advisories/GHSA-4m7w-qmgq-4wj5Third Party Advisory
Other vulnerabilities in aiohttp
- 8.7 High severity
- 8.7 High severity
- 8.3 High severity
- 8.2 High severity
- 7.5 High severity
- 8.7 High severity
Recent Improper Validation of Certificate with Host Mismatch vulnerabilities
- 7.4 High severity
- 8.5 High severity
- 7.3 High severity
- 8.1 High severity
- 7.4 High severity
- 9.1 Critical severity
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