CVE-2026-45809 is a stack-based buffer overflow in OpenSIPS watcherinfo XML generation. When a SIP SUBSCRIBE request arrives with an abnormally long URI in the From header, the presence module stores it without practical length limits. Later, when processing a watcherinfo (winfo) request for that presentity, the XML generation code copies the URI into a fixed-size stack buffer without bounds checking, causing overflow. The vulnerability is exploitable only when the presence.winfo module is loaded—a configuration that's common in deployments serving presence notifications but not universal. Check your opensipsctlrc or equivalent configuration: if loadmodule "presence_winfo.so" appears (uncommented), your deployment is exposed. The presence module itself requires no configuration change to trigger the bug; an attacker simply sends a SUBSCRIBE with a sufficiently large From URI to any user on your system, then requests watcherinfo for that user. The CVSS score of 8.7 reflects moderate exploitability, but the actual risk scales with deployment size: a carrier-grade system handling thousands of concurrent subscriptions becomes a high-value single-packet crash target, whereas a small PBX sees more contained exposure. More critically, treat this as a class vulnerability, not an isolated incident. The presence module stores data that flows to multiple downstream consumers—notify generation, dialog state, event routing. A bounds check in watcherinfo XML generation fixes this specific overflow point but leaves the underlying pattern intact: unbounded input accepted, fixed-buffer consumption downstream, no enforced contract between them. Audit any custom modules or scripts that consume presence data for similar assumptions about URI length. If you're running OpenSIPS 3.6.5 or earlier, upgrade to 3.6.6 immediately. If you cannot upgrade and don't require presence.winfo, unload the module as a temporary mitigation—but recognize this only removes one consumption path, not the underlying storage model.
CVE-2026-45809
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedOpenSIPS is a Session Initiation Protocol (SIP) server implementation. Versions prior to 3.6.6 and 4.0.0-rc1 contain a denial of service vulnerability in the watcherinfo generation functionality. An attacker can create an oversized watcher entry by sending a SUBSCRIBE Event: presence request with a long From URI, and then trigger presence.winfo watcherinfo XML generation for the same presentity. OpenSIPS copies the stored watcher URI into a fixed-size stack buffer, overflowing it and crashing the process. A remote attacker can crash an OpenSIPS worker in deployments that expose handle_subscribe() and allow watcherinfo (presence.winfo) generation. The issue is configuration-dependent because the presence and presence_xml modules must be loaded and SUBSCRIBE routing must be reachable. This issue has been fixed in versions 3.6.6 and 4.0.0-rc1.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysisData overflows a fixed-size buffer allocated on the stack, overwriting adjacent stack memory — including saved return addresses — which is the classic route to redirecting execution into attacker-supplied code. Crafted input is all it takes. Remediation is strict length checks, safe bounded string and memory functions, and modern stack-protection mitigations.
General guidance for the stack-based buffer overflow class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- Authentication
- X
- User interaction
- None
- Scope
- X
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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:X
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped3.6.6 or 4.0.0-rc1
- 1. Identify the current OpenSIPS version by running 'opensips -V' or checking the package manager
- 2. Download the fixed version (3.6.6 for stable 3.x branch or 4.0.0-rc1 for 4.x branch) from the official OpenSIPS download page or repository
- 3. Back up the current OpenSIPS configuration files (/etc/opensips/ by default) and the database if used
- 4. Stop the OpenSIPS service: 'systemctl stop opensips' or 'service opensips stop'
- 5. Install the new version using the package manager or compile from source
- 6. Verify the presence and presence_xml modules are loaded in opensips.cfg if not already configured
- 7. Start the OpenSIPS service: 'systemctl start opensips' or 'service opensips start'
- 8. Verify the service is running and check logs for any errors
Generated from the published advisory — verify against the referenced sources before acting.
There is no version to upgrade to and no patch to apply. Every affected install stays exposed until the vendor ships a fix — or somebody else builds one.
Free. We build fixes in the order the community asks for them — and we’ll tell you the moment this one lands.
We develop and verify an original fix where the vendor hasn’t, from $1,950. Deployed to your staging first — never straight to production.
Scope it with usSee what else the community needs solved on the solutions-needed board.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-45809 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesCVE-2026-45809 is a stack-based buffer overflow in OpenSIPS watcherinfo XML generation. When a SIP SUBSCRIBE request arrives with an abnormally long URI in the From header, the presence module stores it without practical length limits. Later, when processing a watcherinfo (winfo) request for that presentity, the XML generation code copies the URI into a fixed-size stack buffer without bounds checking, causing overflow. The vulnerability is exploitable only when the presence.winfo module is loaded—a configuration that's common in deployments serving presence notifications but not universal. Check your opensipsctlrc or equivalent configuration: if loadmodule "presence_winfo.so" appears (uncommented), your deployment is exposed. The presence module itself requires no configuration change to trigger the bug; an attacker simply sends a SUBSCRIBE with a sufficiently large From URI to any user on your system, then requests watcherinfo for that user. The CVSS score of 8.7 reflects moderate exploitability, but the actual risk scales with deployment size: a carrier-grade system handling thousands of concurrent subscriptions becomes a high-value single-packet crash target, whereas a small PBX sees more contained exposure. More critically, treat this as a class vulnerability, not an isolated incident. The presence module stores data that flows to multiple downstream consumers—notify generation, dialog state, event routing. A bounds check in watcherinfo XML generation fixes this specific overflow point but leaves the underlying pattern intact: unbounded input accepted, fixed-buffer consumption downstream, no enforced contract between them. Audit any custom modules or scripts that consume presence data for similar assumptions about URI length. If you're running OpenSIPS 3.6.5 or earlier, upgrade to 3.6.6 immediately. If you cannot upgrade and don't require presence.winfo, unload the module as a temporary mitigation—but recognize this only removes one consumption path, not the underlying storage model.
Practitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-45809 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data