CVE-2026-1527: medium-severity vulnerability in undici
undici is vulnerable to CRLF Injection via upgrade option
Published · Updated
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13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 4.6epss 0.3%
ImpactWhen an application passes user-controlled input to the upgrade option of client.request(), an attacker can inject CRLF sequences (\r\n) to:
* Inject arbitrary HTTP headers
* Terminate the HTTP request prematurely and smuggle raw data to non-HTTP services (Redis, Memcached, Elasticsearch)
The vulnerability exists because undici writes the upgrade value directly to the socket without validating for invalid header characters:
// lib/dispatcher/client-h1.js:1121
if (upgrade) {
header += `connection: upgrade\r\nupgrade: ${upgrade}\r\n`
}
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
Affected products
undici · undiciRelated CVEs — undici
In the same product, most dangerous first.
CVE-2026-1526HIGHundici is vulnerable to Unbounded Memory Consumption in undici WebSocket permessage-deflate DecompressionEPSS 1.3%CVE-2026-2229HIGHundici is vulnerable to Unhandled Exception in undici WebSocket Client Due to Invalid server_max_window_bits ValidationEPSS 1.0%CVE-2026-12151HIGHundici WebSocket client vulnerable to denial of service via fragment count bypassEPSS 0.8%CVE-2026-2581MEDIUMundici is vulnerable to Unbounded Memory Consumption in in Undici's DeduplicationHandler via Response Buffering leads to DoSEPSS 0.6%CVE-2026-13697HIGHundici vulnerable to cross-user information disclosure and parse-time crash via degenerate private cache directivesEPSS 0.6%CVE-2026-1528HIGHundici is vulnerable to Malicious WebSocket 64-bit length overflows undici parser and crashes the clientEPSS 0.6%