Bug 2458519 (CVE-2026-4893) - CVE-2026-4893 dnsmasq: Broken ECS source validation bypass
Summary: CVE-2026-4893 dnsmasq: Broken ECS source validation bypass
Keywords:
Status: NEW
Alias: CVE-2026-4893
Deadline: 2026-05-09
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Product Security DevOps Team
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-04-14 22:55 UTC by OSIDB Bzimport
Modified: 2026-05-12 16:59 UTC (History)
3 users (show)

Fixed In Version:
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Description OSIDB Bzimport 2026-04-14 22:55:42 UTC 
In forward.c:724, process_reply() calls check_source(header, plen, pheader, query_source) but plen at this point holds the OPT record length (~23 bytes), not the packet length n. With the wrong length, all bounds checks inside check_source() fail and the function unconditionally returns 1, bypassing RFC 7871 Section 9.2 ECS source validation entirely. Fix: change plen to n in the function call.
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