CVE-2025-65570: A type confusion in jsish 2.0 allows incorrect control flow during execution of the OP_NEXT opcode

This week

CRITICAL 9.8REMOTEDOWNGRADE

CVE-2025-65570 is a critical-severity flaw (CVSS 9.8) affecting jsish. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A type confusion in jsish 2.0 allows incorrect control flow during execution of the OP_NEXT opcode. When an “instanceof” expression uses an array element access as the left-hand operand inside a for-in loop, the instructions implementation leaves an additional array reference on the stack rather than consuming it during OP_INSTANCEOF. As a result, OP_NEXT interprets the array as an iterator object and reads the iterCmd function pointer from an in

Why this priority

Critical severity
Public exploit reference
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 55%)
CISA exploited list	No
Weakness	CWE-843
Published	2025-12-29
Last modified	2026-10-13

Publisher (CNA): MITRE · Vendor: jsish

Last updated 2026-10-13 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-12-29 15:16 UTCPublished CVE record published
2026-10-13 09:10 UTCUpdated Record last modified

jsish jsish DOWNGRADE

Affected: 2.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.0

1. Check installed version

apt-cache policy jsish || rpm -q jsish || jsish --version

2. No fixed release: DOWNGRADE to a release before 2.0 (Debian / Ubuntu)

apt-cache madison jsish sudo apt install jsish=<VERSION_BEFORE_2.0> sudo apt-mark hold jsish

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list jsish sudo dnf downgrade jsish-<VERSION_BEFORE_2.0> sudo dnf versionlock add jsish

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora ELN · jgmenu · FIXED · 4.7.0-1.eln159 · FEDORA-2026-40fa69cb49 · source

sudo dnf upgrade --advisory=FEDORA-2026-40fa69cb49

Fedora 46 · trustedqsl · FIXED · 2.8.7-1.fc46 · FEDORA-2026-6b1bc90ebc · source

sudo dnf upgrade --advisory=FEDORA-2026-6b1bc90ebc

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: blog.mcsky.ro/writeups/2025/11/15/inline8-writeup.html

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-65570?

jsish: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2025-65570 being exploited?

CVE-2025-65570 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-65570 affect?

CVE-2025-65570 affects jsish. Severity is critical (CVSS 9.8). A type confusion in jsish 2.0 allows incorrect control flow during execution of the OP_NEXT opcode. When an “instanceof” expression uses an array element access as the left-hand operand inside a for-in loop, the instructions implementation

How urgent is CVE-2025-65570?

Priority 58/100. Critical severity; Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

References

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