CVE-2020-5207 json
Request smuggling is possible in Ktor when both chunked TE and content length specified
published 2020-01-27 6 y ago modified 2026-07-08 4 mo ago also GHSA-xrr9-rh8p-433v , EUVD-2020-0284
- cvss
- 5.4
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.8%
- EPSS 0.8% chance of exploitation in 30 days, percentile 55%
- public exploits
- 0
- none known
Summary
In Ktor before 1.3.0, request smuggling is possible when running behind a proxy that doesn't handle Content-Length and Transfer-Encoding properly or doesn't handle \n as a headers separator.
Patch / fix
- maven io.ktor:ktor-client-cio 1.3.0
- maven io.ktor:ktor-server-cio 1.3.0
- jetbrains ktor 1.3.0
- github.com/ktorio/ktor#1547 pull request
Exploit prediction
0.76% chance of exploitation in the next 30 days, higher than 55% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N |
| NVD | 3.1 | 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N |
| NVD | 2.0 | 5.0 | AV:N/AC:L/Au:N/C:N/I:P/A:N |
| GitHub | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| maven | io.ktor:ktor-client-cio | <1.3.0 |
1.3.0 |
| maven | io.ktor:ktor-server-cio | <1.3.0 |
1.3.0 |
Affected products
- Ktor.io Ktor
Classification
- Weakness
-
- CWE-444 Inconsistent Interpretation of HTTP Requests
References
-
github.com
/ktorio/ktor/pull/1547
web, patch, third-party-advisory
-
github.com
/ktorio/ktor/security/advisories/GHSA-xrr9-rh8p-433v
web, third-party-advisory
-
nvd.nist.gov
/vuln/detail/CVE-2020-5207
advisory
Sources
- CVE List CVE-2020-5207
- GitHub Advisory GHSA-xrr9-rh8p-433v
- NVD CVE-2020-5207
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.