CVE-2019-14853

An error-handling flaw was found in python-ecdsa before version 0.13.3. During signature decoding, malformed DER signatures could raise unexpected exceptions (or no exceptions at all), which could lead to a denial of service.

An error-handling flaw was found in python-ecdsa before version 0.13.3. During signature decoding, malformed DER signatures could raise unexpected exceptions (or no exceptions at all), which could lead to a denial of service.

possible DoS in signature verification and signature malleability

Impact

Code using VerifyingKey.verify() and VerifyingKey.verify_digest() may receive exceptions other than the documented BadSignatureError when signatures are malformed. If those other exceptions are not caught, they may lead to program termination and thus Denial of Service

Code using VerifyingKey.verify() and VerifyingKey.verify_digest() with sigdecode option using ecdsa.util.sigdecode_der will accept signatures even if they are not properly formatted DER. This makes the signatures malleable. It impacts only applications that later sign the signatures or verify signatures of signatures, e.g. Bitcoin.

All versions between 0.5 and 0.13.2 (inclusive) are thought to be vulnerable. Code before 0.5 may be vulnerable but didn't receive extended analysis to rule this issue out.

Patches

The patches have been merged to master branch in https://github.com/warner/python-ecdsa/pull/115. The backported patches for a release in the 0.13 branch are in https://github.com/warner/python-ecdsa/pull/124

They are part of the 0.13.3 release.

There are no plans to backport them to earlier releases.

Workarounds

It may be possible to prevent the Denial of Service by catching also UnexpectedDER, IndexError and AssertionError exceptions. That list hasn't been verified to be complete though. If those exceptions are raised, the signature verification process should consider the signature to be invalid.

To remediate signature malleability and the Denial of Service vulnerability, it may be possible to first verify that the signature is properly DER formatted ECDSA-Sig-Value, as defined in RFC3279, before passing it to verify() or verify_digest() methods. If the signature is determined to not follow the DER or encode a different structure, the signature verification process should consider the signature to be invalid.

References

https://en.bitcoinwiki.org/wiki/Transaction_Malleability

For more information

If you have any questions or comments about this advisory please open an issue in python-ecdsa project.

An error-handling flaw was found in python-ecdsa before version 0.13.3. During signature decoding, malformed DER signatures could raise unexpected exceptions (or no exceptions at all), which could lead to a denial of service.

Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-pwfw-mgfj-7g3g. This link is maintained to preserve external references.

Updated python-ecdsa packages fix security vulnerabilities:

It was discovered that python-ecdsa incorrectly handled certain signatures. A remote attacker could possibly use this issue to cause python-ecdsa to generate unexpected exceptions, resulting in a denial of service (CVE-2019-14853).

It was discovered that python-ecdsa incorrectly verified DER encoding in signatures. A remote attacker could use this issue to perform certain malleability attacks (CVE-2019-14859).

This update for python-ecdsa to version 0.13.3 fixes the following issues:

Security issues fixed:

• CVE-2019-14853: Fixed unexpected exceptions during signature decoding (bsc#1153165).
• CVE-2019-14859: Fixed a signature malleability caused by insufficient checks of DER encoding (bsc#1154217).

This update was imported from the SUSE:SLE-15:Update update project.

This update for python-ecdsa to version 0.13.3 fixes the following issues:

Security issues fixed:

• CVE-2019-14853: Fixed unexpected exceptions during signature decoding (bsc#1153165).
• CVE-2019-14859: Fixed a signature malleability caused by insufficient checks of DER encoding (bsc#1154217).

This update was imported from the SUSE:SLE-15:Update update project.

These are all security issues fixed in the python36-ecdsa-0.16.1-1.5 package on the GA media of openSUSE Tumbleweed.

These are all security issues fixed in the python310-ecdsa-0.19.0-1.1 package on the GA media of openSUSE Tumbleweed.

These are all security issues fixed in the python313-ecdsa-0.19.2-2.2 package on the GA media of openSUSE Tumbleweed.

An error-handling flaw was found in python-ecdsa before version 0.13.3. During signature decoding, malformed DER signatures could raise unexpected exceptions (or no exceptions at all), which could lead to a denial of service.

This update for python-ecdsa to version 0.13.3 fixes the following issues:

Security issues fixed:

• CVE-2019-14853: Fixed unexpected exceptions during signature decoding (bsc#1153165).
• CVE-2019-14859: Fixed a signature malleability caused by insufficient checks of DER encoding (bsc#1154217).

This update for python-ecdsa to version 0.13.3 fixes the following issues:

Security issues fixed:

• CVE-2019-14853: Fixed unexpected exceptions during signature decoding (bsc#1153165).
• CVE-2019-14859: Fixed a signature malleability caused by insufficient checks of DER encoding (bsc#1154217).

This update for python-ecdsa to version 0.13.3 fixes the following issues:

Security issues fixed:

• CVE-2019-14853: Fixed unexpected exceptions during signature decoding (bsc#1153165).
• CVE-2019-14859: Fixed a signature malleability caused by insufficient checks of DER encoding (bsc#1154217).

It was discovered that python-ecdsa incorrectly handled certain signatures. A remote attacker could possibly use this issue to cause python-ecdsa to generate unexpected exceptions, resulting in a denial of service. (CVE-2019-14853)

It was discovered that python-ecdsa incorrectly verified DER encoding in signatures. A remote attacker could use this issue to perform certain malleability attacks. (CVE-2019-14859)