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GHSA-x462-89pf-6r5h

HighCVSS 7.5 / 10
Published May 21, 2021·Last modified Mar 13, 2026
Affected Components(0)

No affected components available

Description

Impact

  1. syncthing can be caused to crash and exit if sent a malformed relay protocol message message with a negative length field.

  2. The relay server strelaysrv can be caused to crash and exit if sent a malformed relay protocol message with a negative length field.

At no point is sensitive data exposed or liable to be altered due to this issue. Sensitive data is never exposed to relay operators. Syncthing itself would need to be lured to connect to a malicious relay server in order to exploit the issue.

Patches

Fixed in version 1.15.0.

Workarounds

  1. No known workaround for strelaysrv.

  2. syncthing can be configured to not use relays, or to only use specific, trusted relays. If Syncthing is used in a closed environment or with relaying disabled, i.e., it does not communicate with unknown relays, Syncthing is not vulnerable.

For more information

If you have any questions or comments about this advisory, please discuss it on the forum.

Thanks to Wojciech Paciorek for discovering and reporting this issue.

Risk Scores
Base Score
7.5

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.

Threat Intelligence
6.9

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
1.97%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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High severity
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