A flaw was found in libsoup

libsoup is GNOME's HTTP client/server library — it ships with GNOME (Epiphany, Evolution, GNOME Online Accounts), gets pulled in by anything linking libsoup-2.4 or libsoup-3, and lives on basically every desktop Linux box and many embedded appliances (Power HMC, IBM appliances, network gear). The flaw is in skip_insignificant_whitespace() inside the content sniffer, which is the routine libsoup uses to guess MIME types from response bodies. A crafted HTTP response from a server can cause the client to read one byte past the end of a heap buffer. Affected: libsoup < 3.6.5 for the 3.x line, plus the legacy 2.4 series that downstreams (Debian, Ubuntu, RHEL, SUSE, Azure Linux) backport into.

Red Hat / GHSA rated this HIGH (7.0) on the back of CVSS C:L/I:L/A:H, because in theory a one-byte over-read can leak adjacent heap metadata or crash the process. In practice it's the client that's vulnerable, the attack complexity is HIGH (the attacker needs to land specific heap layout and serve a malicious response that the client actually content-sniffs), and the realistic outcome is a process crash or at best a one-byte info leak — not RCE. The vendor score is generous; reality is closer to MEDIUM.

Why this verdict

• Client-side only. libsoup is overwhelmingly an HTTP client library; the vulnerable code runs in the victim parsing an attacker-controlled response, not in a server attackers can scan for.
• AC:H is real here. A one-byte over-read requires the attacker to win a heap-layout lottery to leak anything useful; against modern glibc allocators, repeatable info leak is improbable.
• Chain ceiling is crash or 1-byte leak. No public research demonstrates RCE; without a second primitive, this does not escalate beyond DoS of a GNOME app or appliance daemon.
• Role multiplier — desktop / GNOME app role: chain succeeds, blast radius = single-user app crash. Not fleet-impacting.
• Role multiplier — Linux appliance (Power HMC, network gear) role: chain succeeds if the appliance's libsoup-using daemon content-sniffs attacker traffic; blast radius = daemon DoS, not RCE. No identity, hypervisor, CI, backup, or kernel-mode security role is canonically built on libsoup, so no CRITICAL floor is triggered.
• EPSS 0.67% and zero KEV signal corroborate that adversaries are not finding this worth weaponizing.

Why not higher?

HIGH would imply a chain ending in code execution or fleet-scale impact. The primitive is one byte of over-read with no published exploitation technique past crash, the affected role spectrum doesn't include canonically high-value-role components (DCs, IdPs, hypervisors, EDRs, CAs), and no role multiplier triggers the HIGH floor.

Why not lower?

LOW would require ignoring that libsoup ships on essentially every Linux desktop and many embedded appliances, and that the crash impact is real (A:H). The breadth of installation plus genuine availability impact keeps this firmly in MEDIUM rather than backlog hygiene.

1. Patch libsoup to ≥ 3.6.5 (or apply distro backport) on workstations and appliances — Primary fix. For MEDIUM verdicts there is no noisgate mitigation SLA — go straight to the noisgate remediation window of ≤ 365 days, but in practice roll this with your normal monthly desktop / appliance patch cycle within 30–60 days since the fix is low-risk.
2. Audit which libsoup consumers in your estate enable the content sniffer — Apps that don't attach SoupContentSniffer to their session aren't reachable via this codepath. Use ldd / lsof to enumerate processes linking libsoup and grep their source / config for sniffer feature use. Prioritize patching for the ones that do.
3. Block outbound HTTP from server-side libsoup consumers to untrusted destinations — If a server-side daemon (a Power HMC, an IoT controller, an automation runner) uses libsoup as a client, restrict its egress to known hosts via firewall / egress proxy so an attacker cannot serve it the malicious response.
4. Enforce HTTPS with certificate validation for all libsoup-driven flows — Removes the MITM variant of step 1, leaving only direct attacker-controlled URLs reachable via phishing or SSRF.

Run on each Linux target as a privileged user (root or sudo). Example: sudo bash check-cve-2025-2784.sh. Detects installed libsoup version across Debian/Ubuntu (apt), RHEL/Rocky/Alma (rpm), and SUSE (zypper), and compares against the 3.6.5 fix or the distro-specific backport.

#!/usr/bin/env bash
# noisgate verifier — CVE-2025-2784 (libsoup heap over-read)
# Exit: 0 PATCHED, 1 VULNERABLE, 2 UNKNOWN
set -u

FIX_3X='3.6.5'
status='UNKNOWN'
details=''

ver_ge() { # ver_ge A B -> 0 if A >= B
  [ "$1" = "$(printf '%s\n%s\n' "$1" "$2" | sort -V | tail -n1)" ]
}

check_pkg() {
  local name="$1" ver="$2"
  details+="$name=$ver "
  case "$name" in
    libsoup-3.0|libsoup3|libsoup-3.0-0)
      if ver_ge "$ver" "$FIX_3X"; then echo PATCHED; else echo VULNERABLE; fi
      ;;
    libsoup-2.4|libsoup2.4-1|libsoup-2_4-1)
      # 2.4 branch only fixed via distro backport — defer to package manager metadata
      echo UNKNOWN
      ;;
    *) echo UNKNOWN ;;
  esac
}

result='UNKNOWN'
if command -v dpkg-query >/dev/null 2>&1; then
  while read -r n v; do
    [ -z "$n" ] && continue
    r=$(check_pkg "$n" "${v%%-*}")
    [ "$r" = VULNERABLE ] && result=VULNERABLE
    [ "$r" = PATCHED ] && [ "$result" != VULNERABLE ] && result=PATCHED
  done < <(dpkg-query -W -f='${Package} ${Version}\n' 'libsoup*' 2>/dev/null)
fi
if command -v rpm >/dev/null 2>&1; then
  while read -r line; do
    n=$(echo "$line" | awk '{print $1}')
    v=$(echo "$line" | awk '{print $2}')
    [ -z "$n" ] && continue
    r=$(check_pkg "$n" "${v%%-*}")
    [ "$r" = VULNERABLE ] && result=VULNERABLE
    [ "$r" = PATCHED ] && [ "$result" != VULNERABLE ] && result=PATCHED
  done < <(rpm -qa --qf '%{NAME} %{VERSION}\n' 'libsoup*' 2>/dev/null)
fi

echo "$result $details"
case "$result" in
  PATCHED) exit 0 ;;
  VULNERABLE) exit 1 ;;
  *) exit 2 ;;
esac

Sources

1. NVD — CVE-2025-2784
2. GitHub Advisory GHSA-5qxx-2mqf-3v7g
3. Red Hat Bugzilla #2358624
4. Ubuntu USN-7432-1
5. SUSE CVE record
6. IBM Power HMC security bulletin
7. Tenable plugin 235431 (Azure Linux 3.0)
8. Snyk SNYK-DEBIAN11-LIBSOUP24-9652816