CVE catalog

CVE-2026-71890

Severity: High · CVSS 8.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber
Published: Oct 3, 2026, 9:17:05 AM UTC
Updated: Oct 3, 2026, 9:17:05 AM UTC
Source: [NVD] · [CVE record]
EPSS: 0.25% · Oct 25, 2026

In Bouncy Castle for Java before 1.86, validation of an MLS (RFC 9420) external commit's proposal list, org.bouncycastle.mls.protocol.Group.validateExternalCachedProposals, counted the proposals by type and bounded the removed leaf index but never established that the removed leaf had anything to do with the joiner. RFC 9420 sec. 12.2 permits at most one Remove proposal in an external commit, with which the joiner removes an old version of themselves, and requires that where one is present the LeafNode in the commit's path field meet the criteria it would have to meet in an Update for the removed leaf, in particular that its credential present identifiers acceptable for the removed participant. The ordinary proposal-list validator's self-remove rule is deliberately not applied on this path, because a resync commit legitimately removes a leaf the joiner owns, but nothing was put in its place. Any party holding the group's public GroupInfo, which is precisely what an external joiner is meant to be given, could therefore commit a Remove naming any member's LeafIndex and have every member apply it, evicting that member and taking over their slot in the ratchet tree. The credential check that should have prevented this existed only in the gRPC interop harness and so protected no other caller of the public Group.externalJoin and Group.handle API. An external commit carrying a Remove is now accepted only when the removed leaf's credential is identical to the one in the joiner's own new leaf, on both the sending and the receiving side.

Vulnerable and fixed packages

Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.

Distribution	Package	Release	Version	Status
Debian	bouncycastle	sid	`1.86.2-1`	fixed
Debian	bouncycastle	forky	`1.86-1`	fixed
Debian	bouncycastle	trixie	`1.80-3`	vulnerable
Debian	bouncycastle	bookworm	`1.72-2`	vulnerable

Fixed-version evidence

Distribution	Package	Type	Release	Fixed version	Urgency	Origin	Bugs
Debian	bouncycastle	source	sid	`1.86-1`	not yet assigned	Not reported	Not reported
Debian	bouncycastle	source	forky	`1.86-1`	not yet assigned	Not reported	Not reported
Debian	bouncycastle	source	trixie	`(unfixed)`	not yet assigned	Not reported	Not reported
Debian	bouncycastle	source	bookworm	`(unfixed)`	not yet assigned	Not reported	Not reported

OpenFactory catalog packages

[Debian 12 (Bookworm)]

[libbcjmail-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbcmail-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbcpg-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbcpkix-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbcprov-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbctls-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
[libbcutil-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12
- 1.72-2 · all · bookworm
  Affected
  nvd · bouncycastle · debian · bookworm; nvd · bouncycastle · debian · 12

[Debian 13 (Trixie)]

[libbcjmail-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbcmail-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbcpg-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbcpkix-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbcprov-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbctls-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
[libbcutil-java]Affected
Source package: [bouncycastle]
Details (2)
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13
- 1.80-3 · all · trixie
  Affected
  nvd · bouncycastle · debian · 13

Observed: Oct 23, 2026, 7:46:37 PM UTC

References

[CERT-Bund public advisories] · [Debian Security Tracker] · [FIRST EPSS] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [SUSE security advisories and VEX]