CVE-2021-26753: NeDi 1.9C allows an authenticated user to inject PHP code in the System Files function on the endpoint /System

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CRITICAL 9.9DOWNGRADE

CVE-2021-26753 is a critical-severity flaw (CVSS 9.9) affecting nedi. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

NeDi 1.9C allows an authenticated user to inject PHP code in the System Files function on the endpoint /System-Files.php via the txt HTTP POST parameter. This allows an attacker to obtain access to the operating system where NeDi is installed and to all application data.

Why this priority

Critical severity
Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.9 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.1% (top 33%)
CISA exploited list	No
Weakness	CWE-863
Published	2021-02-12
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: nedi

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-02-12 21:15 UTCPublished CVE record published
2026-06-17 03:43 UTCUpdated Record last modified

nedi nedi DOWNGRADE

Affected: 1.9c

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.9c

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 1.9c (Debian / Ubuntu)

apt-cache madison nedi sudo apt install nedi=<VERSION_BEFORE_1.9c> sudo apt-mark hold nedi

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

dnf --showduplicates list nedi sudo dnf downgrade nedi-<VERSION_BEFORE_1.9c> sudo dnf versionlock add nedi

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.

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-2021-26753?

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

Is CVE-2021-26753 being exploited?

CVE-2021-26753 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-2021-26753 affect?

CVE-2021-26753 affects nedi. Severity is critical (CVSS 9.9). NeDi 1.9C allows an authenticated user to inject PHP code in the System Files function on the endpoint /System-Files.php via the txt HTTP POST parameter. This allows an attacker to obtain access to the operating system where NeDi is install

How urgent is CVE-2021-26753?

Priority 56/100. Critical severity; Public exploit reference

Software pages

PHP vulnerabilities

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References

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