UBUNTU-CVE-2025-31498

c-ares is an asynchronous resolver library. From 1.32.3 through 1.34.4, there is a use-after-free in readanswers() when processanswer() may re-enqueue a query either due to a DNS Cookie Failure or when the upstream server does not properly support EDNS, or possibly on TCP queries if the remote closed the connection immediately after a response. If there was an issue trying to put that new transaction on the wire, it would close the connection handle, but read_answers() was still expecting the connection handle to be available to possibly dequeue other responses. In theory a remote attacker might be able to trigger this by flooding the target with ICMP UNREACHABLE packets if they also control the upstream nameserver and can return a result with one of those conditions, this has been untested. Otherwise only a local attacker might be able to change system behavior to make send()/write() return a failure condition. This vulnerability is fixed in 1.34.5.

References

Affected packages

Ubuntu:25.04 / c-ares

Package

Name: c-ares
Purl: pkg:deb/ubuntu/c-ares@1.34.4-2.1ubuntu0.1?arch=source&distro=plucky

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0Unknown introduced version / All previous versions are affected

Fixed

1.34.4-2.1ubuntu0.1

Affected versions

1.*

1.33.0-1

1.34.2-1

1.34.3-1

1.34.4-1

1.34.4-2.1

Ecosystem specific

{
    "binaries": [
        {
            "binary_name": "libc-ares-dev",
            "binary_version": "1.34.4-2.1ubuntu0.1"
        },
        {
            "binary_name": "libc-ares2",
            "binary_version": "1.34.4-2.1ubuntu0.1"
        },
        {
            "binary_name": "libcares2",
            "binary_version": "1.34.4-2.1ubuntu0.1"
        },
        {
            "binary_name": "libcares2-dbgsym",
            "binary_version": "1.34.4-2.1ubuntu0.1"
        }
    ],
    "availability": "No subscription required"
}