Race condition when flushing input stream leads to permission prompt bypass

published 2024-04-18 2 y ago modified 2026-07-18 3 mo ago also EUVD-2024-30286 , JLSEC-2026-106

cvss: 7.7; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 27%
public exploits: 0; none known

Deno is a JavaScript, TypeScript, and WebAssembly runtime with secure defaults. By using ANSI escape sequences and a race between `libc::tcflush(0, libc::TCIFLUSH)` and reading standard input, it's possible to manipulate the permission prompt and force it to allow an unsafe action regardless of the user input. Some ANSI escape sequences act as a info request to the master terminal emulator and the terminal emulator sends back the reply in the PTY channel. standard streams also use this channel to send and get data. For example the `\033[6n` sequence requests the current cursor position. These sequences allow us to append data to the standard input of Deno. This vulnerability allows an attacker to bypass Deno permission policy. This vulnerability is fixed in 1.42.2.

Patch / fix

fixed in 2

julia Deno_jll 2.0.0+0
deno deno 1.42.2

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: partial
Assessed: 2 y ago (2024-04-22)

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 27% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/denoland/deno/security/advisories/GHSA-95cj-3hr2-7j5j referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	7.7	CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD	3.1	7.4	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
OSV	3.1	7.4	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected packages

ecosystem	package	affected	fixed in
julia	Deno_jll	<2.0.0+0	2.0.0+0

Affected products

denoland deno
deno deno

Classification

Weakness

CWE-78 Improper Neutralization of Special Elements used in an OS Command
CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization

References

github.com /denoland/deno/security/advisories/GHSA-95cj-3hr2-7j5j
exploit, vendor-advisory, web

Sources

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.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.

Summary