[CVE-2021-25214] A broken inbound incremental zone update (IXFR) can cause named to terminate unexpectedly

CVE-specific actions

• Assign a CVE identifier
• Determine CVSS score
• Determine the range of BIND versions affected (including the Subscription Edition)
• Determine whether workarounds for the problem exists
• Prepare a detailed description of the problem which should include the following by default:
  • instructions for reproducing the problem (a system test is good enough)
  • explanation of code flow which triggers the problem (a system test is not good enough)
• Prepare a private merge request containing the following items in separate commits:
  • a test for the issue (may be moved to a separate merge request for deferred merging)
  • a fix for the issue
  • documentation updates (CHANGES, release notes, anything else applicable)
• Ensure the merge request from the previous step is reviewed by SWENG staff and has no outstanding discussions
• Ensure the documentation changes introduced by the merge request addressing the problem are reviewed by Support and Marketing staff
• Prepare backports of the merge request addressing the problem for all affected (and still maintained) BIND branches (backporting might affect the issue's scope and/or description)
• Prepare a standalone patch for the last stable release of each affected (and still maintained) BIND branch

Release-specific actions

• Create/update the private issue containing links to fixes & reproducers for all CVEs fixed in a given release cycle: isc-private/bind9#36
• Reserve a block of CHANGES placeholders once the complete set of vulnerabilities fixed in a given release cycle is determined
• Ensure the merge requests containing CVE fixes are merged into security-* branches in CVE identifier order

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A customer has reported the following crash in 9.11.22-S1:

02-Feb-2021 10:00:48.027 general: critical: zone.c:12360: fatal error:
02-Feb-2021 10:00:48.027 general: critical: RUNTIME_CHECK(dbsoacount > 0U) failed
02-Feb-2021 10:00:48.027 general: critical: exiting (due to fatal error in library)

At this time the only other information known is that happened on one of the "DNS servers which are used for ENUM".