GHSA-65pc-fj4g-8rjx CVE-2026-45409 PYSEC-2026-215
Internationalized Domain Names in Applications (IDNA): Specially crafted inputs to idna.encode() can bypass CVE-2024-3651 fix
- Severity
- 6.9 / 10
- Medium · CVSS 4.0
- Exploit chance (EPSS)
- 0.41%
- Chance of exploitation in the next 30 days. Higher than 35.09% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-1333 Inefficient Regular Expression Complexity
- Fix
3.15- Upgrade idna to this version or later
Description
This is the same issue as CVE-2024-3651, however the original remediation in 2024 was not a complete fix. Payloads such as "\u0660" * N or "\u30fb" * N + "\u6f22" utilize the valid_contexto function prior to length rejection, and for high values of N will take a long time to process.
Impact
A specially crafted argument to the idna.encode() function could consume significant resources. This may lead to a denial-of-service.
Patches
Starting in version 3.14, the function rejects long inputs as soon as practicable prior to any further processing to minimize resource consumption. In version 3.15, this approach was extended to lesser used alternate functions (i.e. per-label conversions and codec support).
Workarounds
Domain names cannot exceed 253 characters in length, if this length limit is enforced prior to passing the domain to the idna.encode() function it should no longer consume significant resources. This is triggered by arbitrarily large inputs that would not occur in normal usage, but may be passed to the library assuming there is no preliminary input validation by the higher-level application.
Affected versions
PyPI
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
idna PyPI → 3.15
- pip
pip install --upgrade "idna>=3.15"- poetry
poetry add "idna>=3.15"- uv
uv add "idna>=3.15"
Severity breakdown
CVSS 4.0 6.9
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- None
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- None
- Integrity (vulnerable system)
- None
- Availability (vulnerable system)
- Low
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
CVSS 3.1 5.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- Low
Weakness
CWE-1333: Inefficient Regular Expression Complexity
The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.
How to prevent it
- Architecture and Design: Use regular expressions that do not support backtracking, e.g. by removing nested quantifiers.
- System Configuration: Set backtracking limits in the configuration of the regular expression implementation, such as PHP's pcre.backtrack_limit. Also consider limits on execution time for the process.
- Implementation: Do not use regular expressions with untrusted input. If regular expressions must be used, avoid using backtracking in the expression.
- Implementation: Limit the length of the input that the regular expression will process.
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-jjg7-2v4v-x38h Internationalized Domain Names in Applications (IDNA) vulnerable to denial of service from specially crafted inputs to idna.encode | Medium | Also affects idna |
| GHSA-7wch-p9px-956x Forge: Regular expression denial of service in PEM decoding (pem.decode) | High | Same weakness, CWE-1333 |
| GHSA-xcq7-p3pf-p88h OpenTelemetry Python: Unbounded tracestate parsing in opentelemetry-api | Medium | Same weakness, CWE-1333 |
| GHSA-xgh8-jp6q-p5x8 Pillow: ReDoS in XbmImagePlugin: 512-byte file stalls Image.open() for minutes | High | Same weakness, CWE-1333 |
| GHSA-rxp7-6hxx-x8q5 ip-address: Address6 matches a zone identifier in quadratic time ahead of its length limit, allowing a single long string to stall the process | Medium | Same weakness, CWE-1333 |
| GHSA-r925-mgvr-h9cc Symfony: ReDoS in HeaderUtils::split() Reachable Through the Cache-Control Request Header | High | Same weakness, CWE-1333 |
| GHSA-4ffr-jq9g-5ffx Nodemailer: Quadratic backtracking in SMTP AUTH mechanism detection regexes allows pre-auth remote denial of service | High | Same weakness, CWE-1333 |
| GHSA-m64x-33q8-m5h7 GitPython parse_actor_and_date() is vulnerable to quadratic backtracking on malformed identity lines | High | Same weakness, CWE-1333 |
Credits: StanFromIreland, kjd
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