# CVE-2026-77643 — Xapian xapian-core

> As of 2026-08-20, CVE-2026-77643 is a MEDIUM-severity vulnerability in Xapian xapian-core, CVSS v3.1 4.4, EPSS 0.1% (5.2th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-77643 as of 2026-08-20; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-08-20

## What is CVE-2026-77643?

A cross-site scripting vulnerability in queryparser/termgenerator_internal.cc in Xapian xapian-core before 2.1.0 and before 1.4.32 exists due to incomplete HTML escaping by Xapian::MSet::snippet(). NOTE: this issue exists because of a missed corner case of CVE-2018-0499.

The record classifies CVE-2026-77643 under weakness class [CWE-79](https://intel.threadlinqs.com/cwe/CWE-79). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs a user to take an action first. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 46 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 4.4 — MEDIUM (`CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:L/I:L/A:N`)
- **EPSS (FIRST):** 0.1% probability of exploitation in the next 30 days, higher than 5.2% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4.4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-08-20

## Is CVE-2026-77643 being exploited?

Weaponised exploit code for CVE-2026-77643 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. It currently carries a trending score of 39 in the Threadlinqs vulnerability feed.

- [trickest/cve](https://github.com/trickest/cve/blob/main/2026/CVE-2026-77643.md) (trickest)

## Affected products and versions

- **Xapian**: xapian-core

## How to fix CVE-2026-77643

No vendor patch reference has been recorded for CVE-2026-77643 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-77643

No threat campaign in the Threadlinqs corpus currently references CVE-2026-77643, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, FIRST EPSS, public proof-of-concept repositories. Last verified by Threadlinqs on 2026-08-22.

**Other references**

- [bugs.debian.org](https://bugs.debian.org/1144490)
- [lists.xapian.org](https://lists.xapian.org/pipermail/xapian-devel/2026-August/003429.html)
- [trac.xapian.org](https://trac.xapian.org/wiki/SecurityFixes/2018-07-02#a2026-08-13update)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-77643
Full detection coverage and IOCs for threats exploiting CVE-2026-77643 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp