CVE-2024-53863

Synapse is an open-source Matrix homeserver. In Synapse versions before 1.120.1, enabling the dynamic_thumbnails option or processing a specially crafted request could trigger the decoding and thumbnail generation of uncommon image formats, potentially invoking external tools like Ghostscript for processing. This significantly expands the attack surface in a historically vulnerable area, presenting a risk that far outweighs the benefit, particularly since these formats are rarely used on the open web or within the Matrix ecosystem. Synapse 1.120.1 addresses the issue by restricting thumbnail generation to images in the following widely used formats: PNG, JPEG, GIF, and WebP. This vulnerability is fixed in 1.120.1.

Impact

In Synapse versions before 1.120.1, enabling the dynamic_thumbnails option or processing a specially crafted request could trigger the decoding and thumbnail generation of uncommon image formats, potentially invoking external tools like Ghostscript for processing.

This significantly expands the attack surface in a historically vulnerable area, presenting a risk that far outweighs the benefit, particularly since these formats are rarely used on the open web or within the Matrix ecosystem.

For a list of image formats, as well as decoding libraries and helper programs used, see the Pillow documentation.

Patches

Synapse 1.120.1 addresses the issue by restricting thumbnail generation to images in the following widely used formats: PNG, JPEG, GIF, and WebP.

Workarounds

• Ensure any image codecs and helper programs, such as Ghostscript, are patched against security vulnerabilities.
• Uninstall unused image decoder libraries and helper programs, such as Ghostscript, from the system environment that Synapse is running in.
  • Depending on the installation method, there may be some decoder libraries bundled with Pillow and these cannot be easily uninstalled.
  • The official Docker container image does not include Ghostscript.

References

• The Pillow documentation includes a list of supported image formats and which libraries or helper programs are used to decode them.

For more information

If you have any questions or comments about this advisory, please email us at security at element.io.

Impact

In Synapse versions before 1.120.1, enabling the dynamic_thumbnails option or processing a specially crafted request could trigger the decoding and thumbnail generation of uncommon image formats, potentially invoking external tools like Ghostscript for processing.

This significantly expands the attack surface in a historically vulnerable area, presenting a risk that far outweighs the benefit, particularly since these formats are rarely used on the open web or within the Matrix ecosystem.

For a list of image formats, as well as decoding libraries and helper programs used, see the Pillow documentation.

Patches

Synapse 1.120.1 addresses the issue by restricting thumbnail generation to images in the following widely used formats: PNG, JPEG, GIF, and WebP.

Workarounds

• Ensure any image codecs and helper programs, such as Ghostscript, are patched against security vulnerabilities.
• Uninstall unused image decoder libraries and helper programs, such as Ghostscript, from the system environment that Synapse is running in.
  • Depending on the installation method, there may be some decoder libraries bundled with Pillow and these cannot be easily uninstalled.
  • The official Docker container image does not include Ghostscript.

References

• The Pillow documentation includes a list of supported image formats and which libraries or helper programs are used to decode them.

For more information

If you have any questions or comments about this advisory, please email us at security at element.io.

Synapse is an open-source Matrix homeserver. In Synapse versions before 1.120.1, enabling the dynamic_thumbnails option or processing a specially crafted request could trigger the decoding and thumbnail generation of uncommon image formats, potentially invoking external tools like Ghostscript for processing. This significantly expands the attack surface in a historically vulnerable area, presenting a risk that far outweighs the benefit, particularly since these formats are rarely used on the open web or within the Matrix ecosystem. Synapse 1.120.1 addresses the issue by restricting thumbnail generation to images in the following widely used formats: PNG, JPEG, GIF, and WebP. This vulnerability is fixed in 1.120.1.

These are all security issues fixed in the matrix-synapse-1.120.2-1.1 package on the GA media of openSUSE Tumbleweed.

It was discovered that Synapse network policies could be bypassed via specially crafted URLs. An attacker could possibly use this issue to bypass authentication mechanisms. (CVE-2023-32683)

It was discovered that Synapse exposed cached device information. An attacker could possibly use this issue to gain access to sensitive information. (CVE-2023-43796)

It was discovered that Synapse could be tricked into rejecting state changes in rooms. An attacker could possibly use this issue to cause Synapse to stop functioning properly, resulting in a denial of service. This issue was only fixed in Ubuntu 20.04 LTS and Ubuntu 22.04 LTS. (CVE-2022-39374)

It was discovered that Synapse stored user credentials in a server's database temporarily. An attacker could possibly use this issue to gain access to sensitive information. This issue was only fixed in Ubuntu 22.04 LTS. (CVE-2023-41335)

It was discovered that Synapse could incorrectly respond to server authorization events. An attacker could possibly use this issue to bypass authentication mechanisms. This issue was only fixed in Ubuntu 22.04 LTS. (CVE-2022-39335)

It was discovered that Synapse could be manipulated to mark messages as read when they had not been viewed. An attacker could possibly use this issue to perform repudiation-based attacks. This issue was only fixed in Ubuntu 22.04 LTS. (CVE-2023-42453)

It was discovered that Synapse had several memory-related issues. An attacker could possibly use this issue to cause Synapse to crash, resulting in a denial of service. This issue was only fixed in Ubuntu 22.04 LTS. (CVE-2024-31208)

It was discovered that Synapse could run external tools due to a unchecked thumbnail rendering routine. An attacker could possibly use this issue to cause Synapse to crash, resulting in a denial of service, or execute arbitrary code. This issue was only fixed in Ubuntu 22.04 LTS. (CVE-2024-53863)